Fuel composition

ABSTRACT

An unleaded gasoline comprising a base blend composition having a MON of at least 80 e.g. 80 to less than 98 for motor gasoline and at least 98 for aviation gasoline, which comprises component (a) at least 5% (by volume of the total composition) of at least one hydrocarbon having the following formula I  
     R—CH 2 —CH(CH 3 )—C(CH 3 ) 2 —CH 3   I  
     wherein R is hydrogen or methyl, especially triptane, and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 12 carbon atoms.  
     The corresponding unleaded formulated gasoline comprises also at least one motor or aviation gasoline additive.  
     The blend or gasoline preferably contains at least one of isopentane, aromatics e.g. toluene, olefins, and oxygenates. The gasolines or blends give rise on combustion to reduced levels of emissions of exhaust gases, in particular carbon dioxide, carbon monoxide, nitrogen oxides and total hydrocarbons.

[0001] This invention relates to a fuel composition, in particular a gasoline composition for use in motor vehicles and aviation gasolines possessing a high octane number suitable for use in piston-driven aircraft.

[0002] If a gasoline engine is run on a fuel which has an octane number lower than the minimum requirement for the engine, knocking will occur. Straight run gasoline has a low motor octane number but may be boosted to the required motor octane number of 82-88 for automotive use by the addition of octane boosters such as tetraethyl lead either alone or with refinery components such as reformate, alkylate, cracked spirit or chemical streams such as toluene, xylene, methyl tertiary butyl ether or ethanol.

[0003] For many years manufacturers of spark ignition combustion engines have been striving for higher efficiency to make optimum use of the hydrocarbon fuels. But such engines require gasolines of higher octane number, which has been achieved in particular by addition of organo lead additives, and latterly with the advent of unleaded gasolines, by addition of MTBE. But combustion of any gasoline gives rise to emissions in the exhaust gases, e.g. of carbon dioxide, carbon monoxide, nitrogen oxides (NOx) and toxic hydrocarbons and such emissions are undesirable.

[0004] Motor gasolines have been discovered having high Octane Number but producing low emissions on combustion.

[0005] Aircraft piston-driven engines operate under extreme conditions to deliver the desired power e.g. high compression ratios. Due to the severity of the conditions e.g. with turbo charging or super charging the engine, aviation piston-driven engines require fuel of a minimum octane level higher than that for automotive internal combustion gasoline engines, in particular at least 98-100. The base fuel of an aviation gasoline has a motor octane number of 90-93. To boost the motor octane number sufficiently to the required level, tetraethyl lead is added to the aviation base fuel. The fuel may contain the organolead and also other octane boosters, such as those described above. Industrial and Engineering Chemistry Vol. 36 No.12 p1079-1084 dated 1944 describes the use of triptane (2,2,3-trimethylbutane) in combination with tetraethyl lead in aviation gasoline. However, the presence of tetraethyl lead is the key to achieving high octane quality in aviation gasolines.

[0006] In modem day formulations tetraethyl lead is always used to boost the octane quality of the aviation gasoline to the desired level. However due to environmental concerns of the effect of lead and its compounds attempts are being made to find an alternative to the use of tetraethyl lead in aviation gasoline. Conventional octane boosters such as ethers, aromatics, such as toluene, and non-lead metal compounds can boost the motor octane number of unleaded motor gasoline sufficiently high enough to achieve the desired value but they do not boost the motor octane number of an unleaded aviation gasoline sufficiently high enough to ensure satisfactory performance or suffer from other significant technical limitations.

[0007] U.S. Pat. No. 5,470,358 describes the use of aromatic amines to boost the motor octane number of unleaded aviation gasoline to at least 98 but many aromatic amines are known to be toxic. They have high boiling points, no supercharge properties and high freezing points; they are also prone to produce gums.

[0008] There remains a need for an unleaded aviation gasoline of sufficiently high octane number suitable for use in piston driven aircraft The present invention provides an unleaded blend composition, particularly for automobile use having a Motor Octane Number (MON) of at least 80 comprising component (a) at least 5% or preferably at least 8 or 10% (by volume of the total composition) of at least one hydrocarbon having the following formula I

R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I

[0009] wherein R is hydrogen or methyl

[0010] and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 12, 4-10 such as 5-10 e.g. 5-8 carbon atoms. In another embodiment component (b) is contained in at least one of isomerate, alkylate, straight run gasoline, light reformate, light hydrocrackate and aviation alkylate. Preferably the composition comprises at least one of an olefin (e.g. in amount of 1-30%) and/or at least one aromatic hydrocarbon (e.g. in amount of 1-50%, especially 3-28%) and/or less than 5% of benzene. The composition may preferably comprise 10-40% triptane, less than 5% benzene and have a Reid Vapour Pressure at 37.8° C. measured according to ASTMD323 of 30-120 kPa. This composition of the invention is usually an unleaded motor gasoline base blend composition.

[0011] The present invention also provides an unleaded formulated motor gasoline which comprises said base composition and at least one motor gasoline additive.

[0012] According to the present invention there is provided an unleaded composition, (especially for use in aviation fuel) having a Motor Octane Number of at least 98, and usually a final Boiling Point of less than 170° C., and preferably a Reid Vapour Pressure at 37.8° C. of between 38-60 kpascals,

[0013] which comprises:

[0014] component (a) at least one hydrocarbon of formula I and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 10 in particular 5 or 6 carbon atoms optionally with at least one other saturated liquid aliphatic hydrocarbon having from 5 to 10 carbon atoms wherein at least 20% or at least 30% by volume of the total composition is a hydrocarbon of formula I. The present invention also provides an unleaded aviation fuel having a Motor Octane Number of at least 98, and having a final boiling point of less than 170° C. which comprises:

[0015] component (a) comprising at least one hydrocarbon of formula I

[0016] and component

[0017] (b) at least one saturated liquid aliphatic hydrocarbon having 5 or 6 carbon atoms wherein at least 20% by volume of the total composition is a hydrocarbon of formula I, together with at least one aviation gasoline additive selected from anti-oxidants, corrosion inhibitors, anti-icing additives and anti-static additives.

[0018] If R is hydrogen the hydrocarbon is triptane. If R is methyl the hydrocarbon is 2,2,3 trimethylpentane. Especially preferred is triptane. Triptane and 2,2,3 trimethylpentane may be used individually or in combination with each other, for example, in a weight ratio of 10:90-90:10, preferably, 30:70-70:30.

[0019] The hydrocarbon of formula I, preferably triptane may be present in amount of 5-95% or 8-90% such as 10-90%, or 15-65% e.g. 10-40% such as 20-35% by volume or 40-90% such as 40-55% or 55-80% or 8-35% such as 8-20% by volume. Unless otherwise stated all percentages in this specification are by volume, and disclosures of a number of ranges of amounts in the composition or gasoline for 2 or more ingredients includes disclosures of all sub-combinations of all the ranges with all the ingredients.

[0020] Triptane or 2,2,3 trimethylpentane may be used in a purity of at least 95% but is preferably used as part of a hydrocarbon mixture e.g. with at least 50% of the compound of formula I. This mixture may be obtained for example by alkylation of an iso alkane e.g. reaction of propene and iso butane or obtained via distillation of the product of a catalytic cracking reaction, e.g. a cracked residue which is an atmospheric or vacuum residue from crude oil distillation, to give a C₄ fraction containing olefin and hydrocarbon, alkylation to produce a C₄₋₉ especially a C₆₋₉ fraction which is distilled to give a predominantly C₈ fraction, which usually contains trimethyl pentanes including 2,2,3 trimethyl pentane and/or 2,3,3 trimethyl pentane. To produce triptane this fraction can be demethylated to give a crude product comprising at least 5% of triptane, which can be distilled to increase the triptane content in the mixture; such a distillate may comprise at least 10% or 20% of triptane and 2,2,3 trimethylpentane but especially at least 50% e.g. 50-90% the rest being predominantly of other aliphatic C7 and C8 hydrocarbons e.g. in amount 10-50% by volume. Triptane may be prepared generally as described in Rec. Trav. Chim. 1939, Vol.58 pp 347-348 by J. P. Wibaut et al, which involves reaction of pinacolone with methyl magnesium iodide followed by dehydration (e.g. with sulphuric acid) to form triptene, which is hydrogenated e.g. by catalytic hydrogenation to triptane. Alternatively triptane and 2,2,3 trimethylpentane may be used in any commercially available form.

[0021] The invention will be further described with triptane exemplifying the compound of formula I but 2,2,3 trimethylpentane may be used instead or as well. The terms mogas and avgas will be used herein for convenience to represent motor gasoline and aviation gasoline respectively.

[0022] The gasoline composition for mogas or avgas use also contains as component (b) at least one liquid saturated hydrocarbon of 4-10 e.g. 5-10 carbons especially predominantly branched chain C₇ or C₈ compounds e.g. iso C₇ or iso C₈. This hydrocarbon may be substantially pure e.g. n-heptane, isooctane or isopentane or a mixture e.g. a distillation product or a reaction product from a refinery reaction e.g. alkylate. The hydrocarbon may have a Motor Octane Number (MON) of 0-60 but preferably has a MON value of 60-96 such as isomerate (bp 25-80° C.). Research Octane Number RON may be 80-105 e.g. 95-105, while the ROAD value (average of MON and RON) may be 60-100.

[0023] For avgas use component (b) is preferably at least one saturated aliphatic liquid hydrocarbon of 4 to 10 preferably 5 to 8 in particular 5 or 6 carbon atoms, alone or with at least one saturated aliphatic liquid hydrocarbon (different from component(a)) having from 4 to 10 carbons in particular 5 to 10 carbon atoms, preferably 5 to 8 carbon atoms, especially in combination with one of 4 carbons.

[0024] Component (b) for use in mogas or avgas may comprise a hydrocarbon component (IV) for mogas or avgas use having boiling point (preferably a final boiling point) higher than, preferably one boiling at least 20° C. more than, the compound of formula I e.g. triptane such as 20-60° C. more than triptane but less than 225° C. e.g. less than 170° C. and usually is of Motor Octane Number of at least 92 e.g. 92-100; such components are usually alkanes of 7-10 carbons especially 7 or 8 carbons, and in particular have at least one branch in their alkyl chain, in particular 1-3 branches, and preferably on an internal carbon atom and especially contain at least one —C(CH₃)₂— group, e.g. isooctane

[0025] The volume amount of the component (b) in total in mogas (or the volume amount of mixtures comprising component (b), such as the total of each of the following (if present) (i)-(iv)) (i) catalytic reformate, (ii) heavy catalytic cracked spirit, (iii) light catalytic cracked spirit and (iv) straight run gasoline in the composition is usually 10-80% e.g. 25-70%, 40-65% or 20-40%, the higher percentages being usually used with lower percentages of component (a).

[0026] Component (b) may be a mixture of the liquid saturated hydrocarbons e.g. a distillation product e.g. naphtha or straight run gasoline or a reaction product from a refinery reaction e.g. alkylate including aviation alkylate (bp 30-190° C.) isomerate (bp 25-80° C.), light reformate (bp 20-79° C.) or light hydrocrackate or a mixture thereof e.g. alkylate and isomerate. The mixture may contain at least 60% or at least 70% w/w e.g. 60-95 or 70-90% w/w liquid saturated aliphatic hydrocarbon.

[0027] Volume amounts in the composition of the invention of the component (b) mixtures (primarily saturated liquid aliphatic hydrocarbon fractions e.g. the total of isomerate, alkylate, naphtha and straight run gasoline (in each case (if any) present in the composition) may be 4-60%, such as 4-25% or preferably 10-55% such as 25-45%. Alkylate or straight run gasoline are preferably present, optionally together but preferably in the absence of the other, in particular in amount of 2-50% such as 10-45 e.g. 10-25%, 25-45% or 25-40%. The compositions of the invention may also comprise naphtha e.g. in volume amount of 0-25% such as 2-25%,10-25% or 2-10%.

[0028] The compositions may comprise a hydrocarbon component (b) e.g. for avgas a component III which is at least one saturated aliphatic hydrocarbon of 4-6 carbons and which is more volatile and has a lower boiling point (preferably a lower final boiling point) than the compound of Formula I in particular one boiling at least 30° C. such as 30-60° C. below that of triptane at atmospheric pressure, and especially is itself of Motor Octane Number greater than 88 in particular at least 90 e.g. 88-93 or 90-92. Examples of the hydrocarbon component e.g. component III include alkanes of 4 or 5 carbons in particular iso-pentane, which may be substantially pure or crude hydrocarbon fraction from alkylate or isomerate containing at least 30% e.g. 30-80% such as 50-70%, the main contaminant being up to 40% mono methyl pentanes and up to 50% dimethyl butanes. The hydrocarbon component e.g. for avgas a component III may be an alkane of boiling point (at atmospheric pressure) 30-60° C. less than that of triptane may be used as sole component III but may be mixed with an alkane of boiling point 60-100° C. less than that of triptane e.g. n and/or iso butane optionally in blends with the C₅ alkane of 99.5:0.5 to 0.5:99.5, e.g. 99.5:0.5 to 70:30 such as 88:12 to 75:25. n Butane alone or mixed with isopentane is preferred for mogas use, especially in the above proportions, and in particular with a volume amount of butane in the composition of up to 20% such as 1-15% e.g. 1-8, 3-8 or 8-15%. For avgas use Iso-pentane alone or mixed with n-butane is preferred, especially in the above proportions, and in particular with a volume amount of butane in the composition of up to 3.5% e.g. 1-3.5% or 2-3.5%.

[0029] Cycloaliphatic hydrocarbons e.g. of 5-7 carbons such as cyclopentane or cyclohexane may be present for mogas but usually in amounts of less than 15% of the total e.g. 1-10%.

[0030] Volume amounts in the composition for mogas of the total of isomerate, alkylate, naphtha, straight run gasoline, 4-6 carbon liquid aliphatic hydrocarbon (as defined above) and cycloaliphatic hydrocarbon (in each case if present) may be 5-60%, such as 8-25%, 15-55% such as 30-50%.

[0031] The gasoline compositions of the invention, in particular the ones for mogas use, also preferably contain at least one olefin, (in particular with one double bond per molecule) which is a liquid alkene of 5-10 e.g. 6-8 carbons, such as a linear or branched alkene e.g. pentene, isopentene hexene, isohexene or heptene or 2 methyl 2 pentene, or a mixture comprising alkenes which may be made by cracking e.g. catalytically or thermally cracking a residue from crude oil, e.g. atmospheric or vacuum residue; the mixture may be heavy or light catalytically cracked spirit (or a mixture there of). The cracking may be steam assisted. Other examples of olefin containing mixtures are “C6 bisomer”, catalytic polymerate, and dimate. The olefinic mixtures usually contain at least 10% w/w olefins, such as at least 40% such as 40-80% w/w. Preferred mixtures are (xi) steam cracked spirit (xii) catalytically cracked spirit (xiii) C6 bisomer and (xiv) catalytic polymerate, though the optionally cracked catalytically spirits are most advantageous. Amounts in the total composition of the olefinic mixtures especially the sum of (xi)-(xiv) (if any present) maybe 0-55, e.g. 10-55 or 18-37 such as 23-35 or 20-55 such as 40-55% Amounts of (xi) and (xii) (if present) in total in the composition are preferably 18-55, such as 18-35, 18-30 or 35-55% (by volume).

[0032] The olefin or mixture of olefins usually has an MON value of 70-90, usually a RON value of 85-95 and a ROAD value of 80-92.

[0033] The volume amount of olefin(s) in total in the motor gasoline composition of the invention may be 0% or 0-30%, e.g. 0.1-30% such as 1-30% in particular 2-25, 5-30, (especially 3-10), 5-18.5, 5-18 or 10-20%. Preferably the composition contains at least 1% olefin and a maximum of 18% or especially a maximum of 14%, but may be substantially free of olefin.

[0034] The compositions suitable for mogas or avgas use may also contain at least one aromatic compound, e.g. a liquid one of 6-9 e.g. 6-8 or 7-9 carbons preferably an alkyl aromatic compound such as toluene (which is preferred) or o, m, or p xylene or a mixture thereof or a trimethyl benzene. The aromatics may have been added as single compounds e.g. toluene, or may be added as an aromatics mixture containing at least 30% w/w aromatic compounds such as 30-100% especially 50-90%. Such mixtures may be made from catalytically reformed or cracked gasoline obtained from heavy naphtha. Example of such mixtures are (xxi) catalytic reformate and (xxii) heavy reformate. Amounts of the single compounds e.g. toluene in the composition suitable for mogas use may be 0-35%, such as 2-33% e.g. 10-33%, while amounts of the aromatics mixtures especially the total of the reformates (xxi) & (xxii) (if any) in such a composition may be 0-50%, such as 1-33% e.g. 2-15% or 2-10% or 15-32% v/v, and total amount of reformates (xxi), (xxii) and added single compounds (e.g. toluene) may be 0-50% e.g. 0.5-20% or 5-40, such as 15-35 or 5-25% v/v. In compositions especially suitable for avgas use the amount of liquid aromatic compound in the composition may be up to 30% by volume of the total e.g. 1-30% or 5-15%.

[0035] The aromatics usually have a MON value of 90-110 e.g. 100-110 and a RON value of 100-120 such as 110-120 and a ROAD value of 95-110. The volume amount of aromatic compounds in the composition suitable for mogas use is usually 0% or 0-50% such as less than 40% or less than 28% or less than 20% such as 1-50%, 2-40%, 3-28%, 4-25%, 5-20% (especially 10-20%), 4-10% or 20-35% especially of toluene. The gasoline composition suitable for mogas or avgas may also be substantially free of aromatic compound. Amounts of aromatic compounds of less than 42%, e.g. less than 35% or especially less than 30% are preferred. Preferably the amount of benzene is less than 5% preferably less than 1.5% or 1% e.g. 0.1-1% of the total volume or less than 0.1% of the total weight of the composition.

[0036] The compositions suitable for mogas or avgas use may also contain at least one oxygenate octane booster, usually an ether, usually of Motor Octane Number of at least 96-105 e.g. 98-103. The ether octane booster is usually a dialkyl ether, in particular an asymmetric one, preferably wherein each alkyl has 1-6 carbons, in particular one alkyl being a branched chain alkyl of 3-6 carbons in particular a tertiary alkyl especially of 4-6 carbons such as tert-butyl or tert-amyl, and with the other alkyl being of 1-6 e.g. 1-3 carbons, especially linear, such as methyl or ethyl. Examples of such oxygenates include methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether and methyl tertiary amyl ether. The oxygenate may also be an alcohol of 1-6 carbons e.g. ethanol.

[0037] The volume amount of the oxygenate in the mogas composition may be 0 or 0-25% such as 1-25%, 2-20%, 2-10% or 5-20% especially 5-15%, but advantageously less than 3% such as 1-3% (especially of MTBE and/or ethanol). The oxygenate may also be substantially absent from the mogas composition or motor gasoline of the invention.

[0038] The composition for avgas use may comprise, apart from a component (I), the hydrocarbon of formula I, a component (II) which is at least one of the known octane boosters described above especially an oxygenate octane booster, as described above.

[0039] At least one component (I) may be present in the composition for avgas use together with at least one component (II) in a combination. The combination may be, for example, triptane together with methyl tertiary butyl ether. The combination may be in a volume ratio of 40:60 to 99:1 e.g. 50:50 to 90:10, preferably 60:40 to 85:15. The volume percentage of ether may be up to 30% of the total composition e.g. 1-30%, such as 1-15% or 5-25%.

[0040] The motor octane number of the aviation gasoline of the invention is at least 98, for example 98-103, preferably 99 to 102. Motor Octane Numbers are determined according to ASTM D 2700-92. The hydrocarbons of formula I may also, especially when present in amount of at least 30% by volume, be used to provide aviation gasolines of the invention with a Performance Number (according to ASTM D909) of at least 130 e.g. 130-170.

[0041] The amount of the hydrocarbon of Formula I alone or with component II may be present in the composition suitable for avgas use in an effective amount to boost the Motor Octane Number to at least 98 and may be in a percentage of from 35-92%, preferably 60-90%, especially 70-90% by volume, based on the total volume of the composition. In particular the compound of formula I is usually in the composition in a percentage of 5-90%, 10-80%, 20-60% more especially 30-50% by volume, based on the total composition, though amounts of the compound of formula I of 10-45% are also very valuable; preferred are 20-90% or 40-90% or 50-90% by volume.

[0042] Component (b) may be a combination of at least one component (III) together with at least one component (IV). The combination may be, for example, butane or isopentane together with iso-octane, and the combination may be in a volume ratio of 10:90 to 90:10, preferably 10:50 to 50:90, especially 15:85 to 35:65, in particular with butane or especially isopentane together with iso-octane. Especially preferred is the combination of isopentane together with iso-octane, in particular, in the above proportions, and optionally butane.

[0043] In another preferred embodiment, triptane and isopentane and optionally n-butane are present in the composition of the invention suitable for avgas use with 80-90% triptane and in particular in relative volume ratios of 80-90:10-15:0-3.5.

[0044] In a preferred embodiment of this invention component (a) e.g. for avgas use is 2,2,3 trimethylbutane and component (b) is isopentane in combination with iso-octane, preferably in relative volume ratios of 10-80:5-25:10:80 in particular 30-50:5-25:35-60 or 15-45:10-18:45-75 or 60-80:10-18:10-25. Especially the composition contains 30-80% of triptane and the isopentane and iso-octane are in a volume ratio of 35-15:65-85.

[0045] In a further preferred embodiment of this invention the composition suitable for avgas use comprises component (a) as 2,2,3 trimethylbutane, methyl tertiary butyl ether and component (b) as isopentane in combination with n-butane, preferably in relative volume ratios of 50-90:5-30:10-15:0.1-3.5 in particular 50-80:10-25:10-15:0.1-3.5.

[0046] For use in avgas preferred compositions may contain 50-95% e.g. 50-80% triptane, 5-25% e.g. 10-25% component (b) e.g. isopentane and 5-30%, for example toluene. The benzene content of the composition is preferably less than 0.1% by volume.

[0047] In another preferred embodiment the composition suitable for avgas may comprise both the aromatic hydrocarbon and the ether. In this case a preferred composition may comprise 45-80% triptane 5-30% ether (with a preferred total of both of 70-85%), 10-25% component (b) (III) e.g. iso-pentane (optionally containing butane) and 5-20% toluene, all by volume.

[0048] The compositions suitable for avgas may also comprise 10-90% e.g. 25-85%, 35-80%, or 35-90% by volume of triptane, 5-75% e.g. 8-55% by volume of a mixture predominantly of iso C₇ and iso C₈ hydrocarbons, but usually with small amounts of iso C₆ and iso C₉ hydrocarbons and 5-40% e.g. 8-40% or 5-35% or 8-25% by volume isopentane. The triptane and mixture may be obtained as a distillation fraction obtained by the processing of crude oil and subsequent reactions as described above.

[0049] Composition suitable for use in formulated avgas may comprise the compound of formula 1 e.g. triptane with as component (b) at least one of isomerate and alkylate especially a cut boiling at 90-170° C. e.g. 95-125° C., especially both, and in particular in volume ratios of 1:4 to 4:1 e.g. 1:1 to 1:3. Examples of such compositions contain (and preferably consist essentially of 40-80% such as 50-70% triptane and 20-60% of said component (b), in particular both isomerate and the alkylate, especially with at least 5% of each e.g. 5-40% such as 5-20% (e.g. of isomerate) and 15-35% (e.g. of alkylate cut).

[0050] Aromatic amines e.g. liquid ones such as aniline or alkyl ones e.g. m-toluidine may be present, if at all, in amount of less than 5% by volume for mogas or avgas, and are preferably substantially absent in compositions for mogas or avgas e.g. less than 100 ppm. The relative volume ratio of the amine to triptane is usually less than 3:1 e.g. less than 1:2.

[0051] The compositions of the invention contains components (a) and (b), and the formulated unleaded motor gasoline also contains at least one motor gasoline additive, for example as listed in ASTM D-4814 the contents of which is herein incorporated by reference or specified by a regulatory body, e.g. US California Air Resources Board (CARB) or Environmental Protection Agency (EPA). These additives are distinct from the liquid fuel ingredients, such as MTBE. Such additives may be the lead free ones described in Gasoline and Diesel Fuel Additives, K Owen, Publ. By J. Wiley, Chichester, UK, 1989, Chapters 1 and 2, U.S. Pat. No. 3,955,938, EP 0233250 or EP 288296, the contents of which are herein incorporated by reference. The additives maybe pre-combustion or combustion additives. Examples of additives are anti-oxidants, such as one of the amino or phenolic type, corrosion inhibitors, anti-icing additives e.g. glycol ethers or alcohols, engine detergent additives such as ones of the succinic acid imide, polyalkylene amine or polyether amine type and anti-static additives such as ampholytic surface active agents, metal deactivators, such as one of thioamide type, surface ignition inhibitors such as organic phosphorus compounds, combustion improvers such as alkali metal salts and alkaline earth metal salts of organic acids or sulphuric acid monoesters of higher alcohols, anti valve seat recession and additives such as alkali metal compounds, e.g. sodium or potassium salts such as borates or carboxylates, and colouring agents, such as azodyes. One or more additives (e.g. 2-4) of the same or different types may be used, especially combinations of at least one antioxidant and at least one detergent additive. Antioxidants such as one or more hindered phenols e.g. ones with a tertiary butyl group in one or both ortho positions to the phenolic hydroxyl group are preferred in particular as described in Ex. 1 hereafter. In particular the additives may be present in the composition in amounts of 0.1-100 ppm e.g. 1-20 ppm of each, usually of an antioxidant especially one or more hindered phenols. Total amounts of additive are usually not more than 1000 ppm e.g. 1-1000 ppm.

[0052] The compositions whether for mogas or avgas and corresponding gasolines are free of organolead compounds e.g. are free of added lead such as less than 0.013 gPb/l, and usually of manganese additives such as manganese carbonyls.

[0053] The composition of the invention for use in avgas may contain at least one aviation gasoline additive, for example as listed in ASTM D-910 or DEF-STAN 91-90; examples of additives are anti-oxidants, corrosion inhibitors, anti-icing additives e.g. glycol ethers or alcohols and anti-static additives, especially antioxidants such as one or more hindered phenols; in particular the additives may be present in the composition in amounts of 0.1-100 ppm e.g. 1-20 ppm, usually of an antioxidant especially one or more hindered phenols. A coloured dye may also be present to differentiate the aviation gasoline from other grades of fuel. The formulated avgas is suitable for use to power piston engine aircraft.

[0054] The compositions and gasolines, especially for mogas may contain up to 0.1% sulphur, e.g. 0.000-0.02% such as 0.002-0.01%w/w.

[0055] The motor gasoline compositions of the invention usually have a MON value of at least 80 e.g. 80-110 or 80-105 such as 98-105 or preferably 80 to less than 98, such as 80-95, 83-93 or 93-98. The RON value is usually 90-120 e.g. 102-120 or preferably 90-102 preferably 90-100 e.g. 90-99, such as 90-93 e.g. 91, or 93-98 e.g. 94.5-97.5, or 97-101 while the ROAD value is usually 85-115 e.g. 98-115 or preferably 85-98 such as 85-95 e.g. 85-90, or 90-95 or 95-98. Preferred gasoline compositions have MON 80-83, RON 90-93, and ROAD 85-90, or MON 83-93, RON 93-98 and ROAD 85-95 or MON 83-93, RON 97-101 and ROAD 90-95. The Net calorific value of the gasoline (also called the Specific Energy) is usually at least 18000 Btu/lb e.g. at least 18500, 18700 or 18,900 such as 18500-19500, such as 18700-19300 or 18900-19200; the calorific value may be at least 42 MJ/kg e.g. at least 43.5 MJ/kg such as 42-45 or 43-45 such as 43.5-44.5 MJ/kg. The gasoline usually has a boiling range (ASTM D86) of 20-225° C., in particular with at least 2% e.g. 2-15% boiling in the range 171-225° C. The gasoline is usually such that at 70° C. at least 10% is evaporated while 50% is evaporated on reaching a temperature in the range 77-120° C. preferably 77-116° C. and by 185° C., a minimum of 90% is evaporated. The gasoline is also usually that 10-50% may be evaporated at 70° C., 40-74% at 100° C., 70-97% at 150° C. and 90-99% may be evaporated at 180° C. The Reid Vapour Pressure of the gasoline at 37.8° C. measured according to ASTM D323 is usually 30-120, e.g. 40-100 such as 61-80 or preferably 50-80, 40-65, e.g. 40-60 or 40-50 Kpa.

[0056] The gasoline compositions, when free of any oxygenates usually have a H:C atom ratio of at least 1.8:1 e.g. at least 2.0:1 or at least 2.1 or 2.2:1, such as 1.8-2.3:1 or 2.0-2.2:1. Advantageously the gasoline composition meets the following criteria. ${{{Atom}\quad H\text{:}C \times \left\lbrack {1 + {oxy}} \right\rbrack \times \left\lbrack {\frac{{Net}\quad {Heat}\quad {of}\quad {Combustion}}{200} + {ROAD}} \right\rbrack} \geq y},$

[0057] wherein Atom H:C is the fraction of hydrogen to carbon in the hydrocarbons in the composition, oxy means the molar fraction of oxygenate, if any in the composition, Net Heat of Combustion is the energy derived from burning 1 lb (454 g) weight of fuel (in gaseous form) in oxygen to give gaseous water and carbon dioxide expressed in Btu/lb units [MJ/kg times 430.35], and y is at least 350, 380, 410 or 430, in particular 350-440 e.g. 380-420 especially 400-420.

[0058] The unleaded aviation gasoline composition of the invention usually has a calorific value (also called Specific Energy) of at least 42 MJ/kg (18075 BTU/lb) e.g. at least 43.5 MJ/kg (18720 BTU/lb) such as 42-46 or 43.5-45 MJ/kg. The gasoline usually has a boiling range (ASTM D86) of 25-170° C. and is usually such that at 75° C. 10-40% by volume is evaporated, at 105° C. a minimum of 50% is evaporated, at 135° C. a minimum of 90% is evaporated; the final boiling point is usually not more than 170° C. preferably 80-130° C. The gasoline usually has a maximum freezing point of −60° C. in particular −40° C. The Reid Vapour Pressure of the gasoline at 37.8° C. measured according to ASTM D323 is usually 30-60 kPa preferably 38-60 e.g. 38-55 or especially 38-49 or 45-55 kPa.

[0059] Preferably the motor gasoline of this invention comprises 10-90% of triptane, 10-80% of component (b), 0-25% naphtha, 0-15% of butane, 5-20% of olefin, 3-28% aromatics and 0-25% oxygenate, in particular with 5-20% aromatics and 5-15% olefins.

[0060] In a preferred embodiment of this invention the motor gasoline of this invention contains 8-65% of triptane (especially 15-35%), 0.1-30% such as 2-25% olefins, especially 3-14% and 0-35% aromatics such as 0-30% e.g. 5-35, 5-20 (especially 5-15%) or 20-30%, and 5-50% component (b) mixtures e.g. 10-45% such as 20-40%. Such gasolines may also contain oxygenates, such as MTBE especially in amount of less than 3% e.g. 0.1-3% and especially contain less than 1.5% benzene e.g. 0.1-1%. Such gasolines preferably have RON of 97-99, MON 87-90 and ROAD values of 92-94.5.

[0061] Examples of motor gasolines of the invention are ones with 5-25% triptane, 5-15% olefins, 15-35% aromatics and 40-65% component (b), in particular 15-25% triptane, 7-15%, olefins 15-25% aromatics and 45-52% component (b) mixture of RON value 96.5-97.5, or 5-15% triptane, 7-15% olefins, 15-25% aromatics and 55-65% compound (b) of RON value 94.5-95.5.

[0062] Examples of motor gasolines of the invention are ones having 1-15% e.g. 3-12% butane, 0-20% e.g. 5-15% ether e.g. MTBE, 20-80 e.g. 25-70% of refinery mixed liquid (usually C₆-C₉) streams (apart from naphtha) (such as mixtures of (i)-(iv) above), 0-25% e.g. 2-25% naphtha, 5-70% e.g. 15-65% triptane, with RON 93-100 e.g. 94-98, MON 80-98 e.g. 83-93 or 93-98, and RVP 40-80 such as 40-65 Kpa. Such gasolines usually contain 1-30% e.g. 2-25% olefins and 2-30% e.g. 4-25% aromatics. Amounts of olefins of 15-25% are preferred for RON values of 94-98 e.g. 94-96 and 2-15% e.g. 2-7% for RON values of 96-100 such as 96-98.

[0063] Other examples of motor fuel compositions of the invention contain 8-18% triptane, 10-50% e.g. 25-40% of total component (b) mixture, 5-40% e.g. 20-35% of total aromatics mixture 15-60, e.g. 15-30% or 40-60% of total olefinic mixture and 0-15% total oxygenate e.g. 3-8% or 8-15%. Especially preferred compositions have 8-18% triptane, 25-40% total mixed component (b) mixture, 20-35% total aromatics, and 15-30% total olefinics, or 8-18% triptane, 1540% total mixed component (b) mixture, 3-25% total aromatics mixture, and 40-60% total olefinic mixture.

[0064] Further examples of motor fuel compositions contain 20-40% triptane, 8-55% of the total component (b) mixture, e.g. 5-25% or 35-55%, and 0 or 5-25% e.g. 18-25% total aromatics mixture, 0-55 especially 10-55 or 40-55% total olefin mixture, especially preferred compositions having 20-40% triptane, 5-25% total component (b) mixtures, 3-25% total aromatics mixture and 40-60% total olefinic mixture, or 20-40% triptane, 35-55% total component (b) mixture 15-30% total aromatics mixture and 0-15% e.g. 5-15% total olefin mixture, or in particular 20-40% triptane, 25-45% or 30-50% total component (b) mixture, 2-15% total aromatics mixture 18-35% total olefins mixture, and especially 3-10% or 5-18% olefins, and 10-35% such as 10-20% aromatics (e.g. 10-18%).

[0065] Example of motor fuel compositions contain 30-55% e.g. 40-55% triptane, 5-30% total component (b) mixture 0-10% total aromatic mixture, 10-45% olefinic mixture and 0-15% oxygenates especially with the total of oxygenates and olefinic mixture of 20-45%. Other examples of fuel compositions contain 55-70% triptane, 10-45% total component b, e.g. 10-25% or 35-45%, and 0-10% e.g. 0 or 0.5-5% total aromatics Mixture, and 0-30% total olefinics mixtures, e.g. 0 or 15-30%, especially 55-70% triptane 10-25% total component (b) 0 or 0.5-5% total aromatics mixture and 15-30% total olefinic mixture.

[0066] Particularly preferred examples of motor fuel composition comprise 15-35% e.g. 20-35% triptane, 0-18.5% e.g. 2-18.5% olefin, 5-40% e.g. 5-35% aromatics 25-65% saturates and less than 1% benzene, and 18-65% e.g 40-65% triptane, 0-18-5% e.g. 5-18.5% olefins, 5-42% e.g. 5-28% aromatics, 35-55% saturates and less than 1% benzene.

[0067] Another motor fuel composition may comprise 25-40% e.g. 30-40% such as 35% of alkylate, 10-25% e.g. 15-25% such as 20% of isomerate, 10-25% e.g. 15-25% such as 20% of light hydrocrackate and 20-35% e.g. 20-30% such as 25% of triptane and optionally 0-5% butane. Such a composition is preferably substantially paraffinic and is substantially free of olefins and aromatics.

[0068] Other motor fuel compositions of the invention may have different ranges of the Antiknock Index (also known as The ROAD Index), which is the average of MON and RON.

[0069] For ROAD Indexes of 85.5-88.5, the compositions suitable for mogas use may comprise 8-30% triptane e.g. 15-30%, and 10-50% e.g. 20-40% total component (b) mixture, 5-30%, e.g. 5-20% total olefins and 10-40 e.g. 15-35% total aromatics, or 8-30% triptane, 10-50% total component (b) mixture, 5-40% total aromatic mixtures e.g. 20-30% and 10-60% e.g. 30-55% total olefinic mixtures.

[0070] For ROAD Indexes of 88.5-91.0 the compositions suitable for mogas use may comprise 5-25% (or 5-15%) triptane, 20-45% total component (b) mixture, 0-25% e.g. 1-10 or 10-25% total olefins, and 10-35% e.g. 10-20% or 20-35% total aromatics or 5-25% (5-15%) triptane, 20-45% total component (b) mixture, 0-35% total aromatic mixtures e.g. 1-15 or 15-35%, and 5-65% e.g. 5-30 or 30-65% total olefinic mixtures.

[0071] For ROAD Indexes of 91.0-94.0 the motor fuel compositions of the invention may comprise 5-65% e.g. 5-20, 20-30, 30-65 or 40-65% triptane and 5-40% (5-35%) e.g. 5-12 or 12-40% (12-30%) total component (b) mixture 1-30% e.g. 1-10 or 10-25% total olefins and 5-55% e.g. 5-15 or 15-35 or 35-55% total aromatics, or the above amounts of triptane with 0-55 e.g. 0.5-25% e.g. 10-25% or 25-55% of aromatic fractions and 0 or 10-60% e.g. 10-30% or 35-60% total olefin fractions.

[0072] For ROAD values of 94-97.9, the motor fuel compositions may comprise 20-65% triptane e.g. 40-65% triptane, 0-15% e.g. 5-15% total olefins, 0-20% e.g. 5-20% total aromatics and 5-50 e.g. 30-50% total component (b) mixture, or the above amounts of triptane and total component (b) mixture with 0-30% e.g. 10-30% aromatic fractions and 0-30 e.g. 5-30% olefinic fraction, or the above amounts of triptane e.g. 20-40% triptane, total component b mixture, total olefins and total aromatics, with 2-15% aromatic fractions and 18-35% olefinic fractions.

[0073] The invention can provide motor gasolines, in particular of 9l, 95, 97, 98 and 10 RON values and aviation gasoline in particular of 99-102 MON values, with desired high Octane Levels but low emission values on combustion in particular of at least one of total hydrocarbons, total air toxics, NOx, carbon monoxide, and carbon dioxide, especially of both total hydrocarbons and NOx. Thus the invention also provides the use of a compound of formula I, in particular triptane, in unleaded motor gasoline of MON at least 80 e.g. 80 to less than 98 or in unleaded aviation gasoline of MON of at least 98, e.g. as an additive to or component therein, to reduce the emission levels on combustion, especially of at least one of total hydrocarbons, total air toxics NOx, carbon monoxide and carbon dioxide especially both of total hydrocarbons and NOx. The invention also provides a method of reducing emissions of exhaust gases in the combustion of unleaded motor gasoline fuels of MON of at least 80 or in unleaded aviation gasoline of MON of at least 98 which comprises having a compound of formula I present in the fuel which is a gasoline of the invention. The invention also provides use of an unleaded gasoline of the invention in a spark ignition combustion engine to reduce emissions of exhaust gases. While the compositions of the invention may be used in supercharged or turbocharged engines, they are preferably not so used, but are used in normally aspirated ones. The compound of formula I e.g. triptane can reduce one or more of the above emission levels especially in mogas better than amounts of alkylate or a mixture of aromatics and oxygenate at similar Octane Number and usually decrease the fuel consumption as well. The compositions and gasolines of the invention are unleaded and can have reduced toxicity compared to ones with aromatic amines or organo leads. According to another aspect of the present invention there is provided an unleaded aviation fuel composition, having a Motor Octane Number of at least 98, and usually a final Boiling Point of less than 200° C. or especially 170° C., and preferably a Reid Vapour Pressure at 37.8° C. of between 35-60 especially 38-60 kpascals, which comprises:

[0074] component (a) at least one hydrocarbon having the following formula I

R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I

[0075] wherein R is hydrogen or methyl

[0076] and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 10 in particular 5 or 6 carbon atoms optionally with at least one other saturated liquid aliphatic hydrocarbon having from 5 to 10 carbon atoms wherein 35-92% especially 40-78% by volume of the total composition is a hydrocarbon of formula I. Unless otherwise stated all percentages in this specification are by volume, and disclosures of a number of ranges of amounts in the composition or gasoline for 2 or more ingredients includes disclosures of all sub-combinations of all the ranges with the ingredients.

[0077] If R is hydrogen the hydrocarbon is triptane. If R is methyl the hydrocarbon is 2,2,3 trimethylpentane. Especially preferred is triptane. Triptane and 2,2,3 trimethylpentane may be used individually or in combination with each other, for example, in a weight ratio of 10:90-90:10, preferably, 30:70-70:30.

[0078] The composition may comprise apart from a component (I), the hydrocarbon of formula I, a component (II) which is at least one of the known octane boosters described above especially an oxygenate octane booster, usually an ether, usually of Motor Octane Number of at least 96-105 e.g. 98-103. The ether octane booster is usually a dialkyl ether, in particular an asymmetric one, preferably wherein each alkyl has 1-6 carbons, in particular one alkyl being a branched chain alkyl of 3-6 carbons in particular a tertiary alkyl especially of 4-6 carbons such as tert-butyl or tert-amyl, and with the other alkyl being of 1-6 e.g. 1-3 carbons, especially linear, such as methyl or ethyl. Examples of component (II) include methyl tertiary butyl ether, ethyl tertiary butyl ether and methyl tertiary amyl ether. Cyclic ethers such as furan, tetra hydro furan and their lower alkyl e.g. methyl derivatives may also be used. The oxygenate may also be an alcohol of 1-6 carbons e.g. ethanol.

[0079] At least one component (I) may be present together with at least one component (II) in a combination. The combination may be, for example, triptane together with methyl tertiary butyl ether. The combination may be in a volume ratio of 40:60 to 99:1 e.g. 50:50 to 90:10, preferably 60:40 to 85:15. The volume percentage of ether may be up to 30% of the total composition e.g. 1-30%, such as 1-15% or 5-25%. The unleaded blend composition may also be substantially free of any oxygenate octane booster e.g. ether or alcohol.

[0080] The motor octane number of the aviation gasoline of the invention is at least 98, for example 98-103, preferably 99 to 102 or especially 100-101.5. Motor Octane Numbers are determined according to ASTM D 2700-92. The hydrocarbons of formula I may also, especially when present in amount of at least 30% by volume, be used to provide gasolines of the invention with a Performance Number (according to ASTM D909) of at least 130 e.g. 130-170.

[0081] Triptane or 2,2,3 trimethylpentane may be used in a purity of at least 95% but is preferably used as part of a hydrocarbon mixture obtained, via distillation of a cracked residue, which is an atmospheric or vacuum residue from crude oil distillation, to give a C₄ fraction containing olefin and hydrocarbon, alkylation to produce a C₄₋₉ especially a C₆₋₉ fraction which is distilled to give a predominantly C₈ fraction, which usually contains trimethyl pentanes including 223 trimethyl pentane and/or 233 trimethyl pentane. To produce triptane this fraction can be

[0082] demethylated to give a crude product comprising at least 5% of triptane, which can be distilled to increase the triptane content in the mixture; such a distillate may comprise at least 10% or 20% of triptane and 2,2,3 trimethylpentane but especially at least 50% e.g. 50-90% the rest being predominantly of other aliphatic C7 and C8 hydrocarbons e.g. in amount 10-50% by volume.

[0083] Triptane may be prepared generally as described in Rec. Trav. Chim. 1939, Vol. 58 pp 347-348 by J P Wibaut et al, which involves reaction of pinacolone with methyl magnesium iodide followed by dehydration (e.g. with sulphuric acid) to form triptene, which is hydrogenated e.g. by catalytic hydrogenation to triptane. Alternatively triptane and 2,2,3 trimethylpentane may be used in any commercially available form.

[0084] The invention will be further described with triptane exemplifying the compound of formula I but 2,2,3 trimethylpentane may be used instead or as well.

[0085] The amount of the hydrocarbon of Formula I alone or with component II may be present in the composition in an effective amount to boost the Motor Octane Number to at least 98 and may be in a percentage of from 35-92%, preferably 60-90%, especially 70-90% by volume, based on the total volume of the composition. In particular the compound of formula I is usually in the composition in a percentage of 30-60% more especially 30-50% by volume, but based on the total composition, preferred are 40-90% or 50-90% or most especially 45-70%.

[0086] The composition also comprises a component (b). Component (b) is at least one saturated aliphatic liquid hydrocarbon of 4 to 10 preferably 5 to 8 in particular 5 or 6 carbon atoms, alone or with at least one saturated aliphatic liquid hydrocarbon (different from component(a)) having from 4 to 10 carbons in particular 5 to 10 carbon atoms, preferably 5 to 8 carbon atoms, especially in combination with one of 4 carbons. Component (b) may comprise a component (III) which is more volatile and has a lower boiling point than component (a) in particular one boiling at least 30° C. such as 30-60° C. below that of triptane at atmospheric pressure, and especially is itself of Motor Octane Number greater than 88 in particular at least 90 e.g. 88-93 or 90-92. Examples of component (III) include alkanes of 5 carbons in particular iso-pentane, which may be substantially pure or a crude hydrocarbon fraction from alkylate or isomerate (eg of Bp 25-80° C.) containing at least 30% e.g. 30-80% such as

[0087] 50-70%, the main contaminant being up to 40% mono methyl pentanes and up to 50% dimethyl butanes. The amount of isopentane in the composition is usually 3-35% eg 5-35, 5-25, 5-15, 10-18% or 1-10% such as 3-10%. When the isopentane is added to make the composition in the form of the crude fraction from alkylate or isomerate with at least 30% isopentane, the volume amount of alkylate fraction or isomerate may be 6-70%, eg 7-50% especially 6-44, eg 6-17 or 10-44%. Component (III) of boiling point 30-60° C. less than that of triptane may be used as sole component (III) but may be mixed with an alkane of boiling point 60-100° C. less than that of triptane e.g. n and/or iso butane in blends of 99.5:0.5 to 50:50 such as 88:12 to 70:30, e.g. 88:12 to 75:25 or 70:30 to 50:50. Iso-pentane alone or mixed with n-butane is preferred, especially in the above proportions. In particular a volume amount of butane in the composition is up to 7% such as up to 6.5 or 5.5% e.g. up to 3.5% e.g. 1-3.5% or 2-3.5%, or 1.5-5.5% or 2-7 such as 3.5-5.5% Component (b) may also comprise a component (IV) having a boiling point higher than component (a) preferably one boiling at least 18° C. more than the compound of formula I e.g. triptane such as 20-60° C. more than triptane but less than 170° C. and usually is of Motor Octane Number of at least 92 e.g. 92-100; such components (IV) are usually alkanes of 7-10 carbons especially 7 or 8 carbons, and in particular have at least one branch in their alkyl chain, in particular 1-3 branches, and preferably on an internal carbon atom and especially contain at least one —C(CH₃)₂— group. An example of component (IV) is iso-octane.

[0088] The amount of component IV in particular isooctane (224 trimethylpentane) in the composition may be zero, but is usually 10-80% eg 12-48%, 10-35, 10-25, 35-60 or 45-75% but may be 1-25% e.g. 1-10% or 5-20%. The component IV especially isooctane may be added as such to form the composition, and/or may be added in the form of a fraction comprising at least 30% of said component IV especially isooctane such as 30-80% such as 40-60%; examples of such as fractions are alkylate fractions eg bp (1 bar pressure) of 85-135° C. and 90-115° C. or 95-105° C. Such fractions may be mixtures predominantly of branched chain eg iso C₈ hydrocarbons (eg at least 50% or 60% of the mixture) especially mixtures predominantly of iso C₇ and iso C₈ hydrocarbons and usually with small amounts (eg 1-20% (of the mixture) of either or both) of iso C₆ and iso C₉ hydrocarbons. Amounts of such fractions in the composition may be 2-55% e.g. be 8-55% e.g. 12-52% or 2-15 or 5-15%. Blends of such fractions with added component IV eg isooctane may be used, in particular with 10-35% IV (eg isooctane) and 5-55% fractions eg alkylate fractions (especially predominantly iso C₈ hydrocarbon) such as 8-25%.

[0089] Component (b) may be a combination of at least one component (III) together with at least one component (IV). The combination may be, for example, butane or isopentane together with iso-octane, and the combination may be in a volume ratio of 10:90 to 90:10, preferably 10:50 to 50:90, especially 15:85 to 35:65 or 15-50:85-50, in particular with butane or especially isopentane together with iso-octane. Especially preferred is the combination of isopentane together with iso-octane, in particular, in the above proportions, and optionally butane.

[0090] In another preferred embodiment, triptane and isopentane and optionally n- butane are present in the composition of the invention with 80-90% triptane and in particular in relative volume ratios of 80-90:10-15:0-3.5.

[0091] In a preferred embodiment of this invention component (a) is 2,2,3 trimethylbutane and component (b) is isopentane in combination with iso-octane, preferably in relative volume ratios of 10-80:5-25:10-80 in particular 30-50:5-25:35-60 or 15-45:10-18:45-75 or 60-80:10-18:10-25. Especially the composition contains 30-80% of triptane and the isopentane and iso-octane are in a volume ratio of 35-15:65-85.

[0092] In a most preferred embodiment the composition of the invention comprises as Component (a) 223 trimethyl butane in an amount of 40-90% and as component (b) an isomerate fraction comprising 30-70% isopentane (the amount of isomerate being 6-47% in the composition, isooctane in amount of 10-35% and 1-3.5% butane, the isooctane being present as such and/or mixed with other hydrocarbons in an isooctane containing fraction. Especially preferred compositions comprise 40-60% triptane, 6-17% isomerate, 10-35% isooctane, 1-3.5% butane, the isooctane being especially at least partly (eg at least 20% such as 30-60%) present in a mixture predominantly of iso C₇ and iso C₈ hydrocarbons, with small amounts of iso C₆ and iso C₉ hydrocarbons (said mixture providing 8-55% of the total volume of the composition).

[0093] In a further preferred embodiment of this invention the composition comprises component (a) as 2,2,3 trimethylbutane, methyl tertiary butyl ether and component (b) as isopentane in combination with n-butane, preferably in relative volume ratios of 50-90:5-30:10-15:0.1-3.5 in particular 50-80:10-25:10-15:0.1-3.5.

[0094] If desired the composition may comprise an aromatic liquid hydrocarbon of 6-9 e.g. 6-8 or 7-9 carbons, such as xylene or a trimethyl benzene, preferably toluene, in particular in amounts of up to 30% by volume of the total composition e.g. 1-30% or 5-30%, such as 5-20% or 5-15% or 1-15% such as 2-15% e.g. 2-10%. In this case a preferred embodiment is a composition that may thus contain 15-95% or 15-90%, 50-95% e.g. 15-80% or 50-80% triptane, 5-25% e.g. 10-25% component (b) e.g. isopentane and 5-30%, for example toluene. The benzene content of the composition is preferably less than 0.1% by volume. The gasoline composition suitable for avgas may also be substantially free of aromatic compound. Amounts of aromatic compounds of less than 42% or 40%, e.g. less than 35% or especially less than 30% or 20% are preferred.

[0095] Preferably the amount of benzene is less than 5% preferably less than 1.5% or 1% e.g. 0.1-1% of the total volume or less than 0.1% of the total weight of the composition. The aromatic hydrocarbon(s) is preferably in an reformate fraction e.g. of bp 100-140° C.

[0096] In another preferred embodiment the composition may comprise both the aromatic hydrocarbon and the ether or just the aromatic hydrocarbon. In this case a preferred composition may comprise 45-80% triptane 0% or 5-30% ether (with a preferred total of both of 70-85%), and either with 10-25% component (b) (III) e.g. isopentane (optionally containing butane) and 5-20% toluene, all by volume, or with 3-15% component (b) III of the total of isopentane and butane (if present) and 2-15% toluene and 1-20% such as 5-15% tert-butyl benzene.

[0097] The compositions may also comprise 10-90% e.g. 25-85%, 35-80%, or 35-90% by volume of triptane, 5-75% e.g. 8-55% by volume of a mixture predominantly of iso C₇ and iso C₈ hydrocarbons, but usually with small amounts of iso C₆ and iso C₉ hydrocarbons and 5-40% e.g. 8-40% or 5-35% or 8-25% by volume isopentane. The triptane and mixture may be obtained as a distillation fraction obtained by the processing of crude oil and subsequent reactions as described above.

[0098] Other compositions of the invention comprise by volume (i) 60-90% e.g. 70-85% triptane, (ii) 2-20% of component III or an alkane of 4-7 carbons (or mixture thereof), at least the majority of which boils below triptane, such as 2-10% isomerate or 5-20% isopentane, (iii) 0 or up to 15% such as 2-15% liquid aromatic hydrocarbon e.g. toluene or xylene or a mixture of hydrocarbons containing at least a majority thereof, e.g. substantially all aromatics as in a reformate fraction (e.g. of boiling point 105-135° C.) and (iv) 0 or up to 15% e.g. 2-15% of component IV which may be isooctane or an alkylate fraction (e.g. of bp 95-105° C.), and (v) 0 or up to 7% e.g. 2-7% butane.

[0099] Composition suitable for use in formulated avgas may comprise the compound of formula 1 e.g. triptane with as component (b) at least one of isomerate and alkylate especially a cut boiling at 90-170° C. e.g. 95-125° C., especially both, and in particular in volume ratios of 1:4 to 4:1 e.g. 1:1 to 1:3. Examples of such compositions contain (and preferably consist essentially of 40-80% such as 50-70% triptane and 20-60% of said component (b), in particular both isomerate and the alkylate, especially with at least 5% of each e.g. 5-40% such as 5-20% (e.g. of isomerate) and 15-35% (e.g. of alkylate cut).

[0100] The compositions of the invention may also contain an aromatic compound containing a benzene nucleus substituted by at least 1 (e.g. 1 or 2 especially 1) branched chain alkyl substituent of 3-5 carbon atoms i.e. a secondary or especially tertiary alkyl group hereinafter called component I¹. More than 1 group may be present of the same or a different type and in o, m or p position. Examples of such groups are isopropyl, isobutyl, secbutyl, tertbutyl, isoamyl, sec amyl, neopentyl and tertamyl; tertiary butyl is preferred, so the preferred compound is tert butyl benzene. The volume amount of this subsituted aromatic compound may be 0% or 1-30% such as 2-25 e.g. 5-15%.

[0101] Examples of unleaded aviation gasoline compositions with such or substituted aromatic compound are ones with 2-7% e.g. 3.5-5.5% butane 0% or 1-15 such as 3-10% isopentane, 50-90% triptane especially 50-70% or 70-90%, 0% or 1-25% e.g. 1-10 or 5-20% or 10-25% isooctane, 0%, 1-15% or 2-15% e.g. 2-10% toluene, 0% or 5-30% asymmetric dialkylether such as methyl tert butyl ether or especially ethyl tert butyl ether, and 1-20% eg. 5-15% tert butyl benzene. Such compositions can have Reid Vapour Pressuer at 37.8° C. of 35-50 kPa, while MON is usually 99.5-104 e.g. 100-102.

[0102] Such branched chain alkyl substituted benzenes are commercial available materials and and may be made by known means. Thus they may be made by alkylation of benzene with an olefin of 3-5 carbons especially one with a branch methyl or ethyl group or an internal olefinic carbon atom e.g. a 2-alkyl substituted olefin e.g. 2-methyl butene 1 (isobutene) or 2 ethyl butene-1 (iso pentene) or propylene. The alkylation is usually in the presence of a Friedel Crafts or Bronsted Acid catalyst e.g. iron or aluminium chloride or sulphuric acid or boron trifluoride. The alkylation gives predominantly monosubstitution especially with the tert butyl group, but there may be some e.g. up to 10% di-substituted product e.g. in o or p position; the crude alkylation product may be used in the gasolines as such or after purification to 95%+purity.

[0103] The unleaded aviation gasoline composition of the invention usually has a net calorific value (also called Specific Energy) of at least 42 MJ/kg (18075 BTU/lb) e.g. at least 43.5 MJ/kg (18720 BTU/lb) such as 42-46 or 43.5-45 MJ/kg. The gasoline usually has a boiling range (ASTM D86) of 25-170° C. and is usually such that at 75° C., 8-40% such as 10-40% or 8-25% by volume is evaporated, at 105° C. a minimum of 50% is evaporated e.g. 50-100 especially 85-100%, at 135° C. a minimum of 90% e.g. 90-100% such as 96-100% is evaporated; the final boiling point is usually not more than 170° C. preferably 80-140° or 80-130° C. The gasoline usually has a maximum freezing point of −40° C., in particular −55 or −60° C. e.g. a freezing point of −40° to −90° C. such as −70 to −90° C. The Reid Vapour Pressure of the gasoline at 37.8° C. measured according to ASTM D323 is usually 30-60 kPa preferably 35-60 e.g. 38-55 or especially 38-49 or 45-55 kPa.

[0104] Unleaded gasoline compositions of the invention comprising a branched chain alkyl substituted benzene as described above usually have a boiling range (ASTM D86) of 30-200° C. e.g. 35-190° C. with an initial boiling point of 35-45° C., and are usually such that the temperature for distillation of 10% of the gasoline is 60-100° C. e.g. 65-80° C. or 80-90° C. the 40% distillation temperature is at least 0.5-8° C. greater e.g. 8-15° C. greater, e.g. 75-110 such as 80-90 or 90-105° C., the 50% distillation temperature is usually at least 0.5° C. higher e.g. 0.5-3° C. higher such as 80-110 such as 81-91 or 95-105° C. the 90% distillation temperature is at least 20° C. higher still e.g.

[0105] 20-120° C. or 20-45° C. or 40-90° C. higher, such as 105-190° C. e.g. 105-130° C. or 130-190° C. such as 105-120° C. or 115-130° C., the sum of the 10% and 50% distillation temperatures are usually 150-200, such as 150-165 or 180-195° C. and the final boiling point of at least 50-75° C. such as 50-65° C. higher than the 90% distillation figure, such as 175-195 e.g. 178-190° C. The freezing point and RVP are usually as described above. These values for the gasolines with the substituted alkyl benzene usually apply whether the gasoline also contains compound (a) e.g. triptane or not.

[0106] The composition of the invention may contain at least one aviation gasoline additive, for example as listed in ASTM D-910 or DEF-STAN 91-90; examples of additives are anti-oxidants, corrosion inhibitors, anti-icing additives e.g. glycol ethers or alcohols and anti-static additives, especially antioxidants such as one or more hindered phenols; in particular the additives may be present in the composition in amounts of 0.1-100 ppm e.g. 1-20 ppm, usually of an antioxidant especially one or more hindered phenols. A coloured dye may also be present to differentiate the aviation gasoline from other grades of fuel.

[0107] Aromatic amines e.g. liquid ones such as aniline or alkyl ones e.g. m-toluidine may be present, if at all, in amount of less than 5% by volume, and are preferably substantially absent in the avgas compositions e.g. less than 100 ppm. The relative volume ratio of the amine to triptane is usually less than 3:1 e.g. less than 1:2. The compositions of the invention may also contain other engine performance enhancing fluids, such as methanol/water mixtures (though these are preferably absent) or maybe used with nitrous oxide injection in the combustion air or cylinder.

[0108] The invention can provide aviation gasoline in particular of 99-102 MON values, with desired high Octane Levels but low emission values on combustion in particular of at least one of total hydrocarbons, total air toxics, NOx, carbon monoxide, and carbon dioxide, especially of both total hydrocarbons and NOx. Thus the invention also provides the use of a compound of formula I, in particular triptane, in unleaded aviation

[0109] gasoline of MON of at least 98, e.g. as an additive to or component therein, to reduce the emission levels on combustion, especially of at least one of total hydrocarbons, total air toxics NOx, carbon monoxide and carbon dioxide especially both of total hydrocarbons and NOx. The invention also provides a method of reducing emissions of exhaust gases in the combustion of unleaded aviation gasoline of MON of at least 98 which comprises having a compound of formula I present in the fuel which is a gasoline of the invention. The invention also provides use of an unleaded gasoline of the invention in a spark ignition combustion engine to reduce emissions of exhaust gases. The invention also provides a method of reducing the exhaust gas temperature of a spark ignition combustion engine (e.g. an aviation engine) which comprises having a compound of formula 1 in the fuel which is combusted. The invention also provides the use of said compound to reduce the exhaust gas temperature of said engine in particular an air cooled aviation engine. In the compositions, gasolines, methods and uses of the invention the hydrocarbon of formula 1, in particular triptane is preferably used in a emission-reducing effective amount, and/or in a exhaust-gas-temperature-reducing effective amount. While the compositions of the invention may be used in supercharged or turbocharged engines, they are preferably not so used, but are used in normally aspirated ones. The compound of formula I e.g. triptane may reduce one or more of the above emission levels better than amounts of alkylate or a mixture of aromatics and oxygenate at similar Octane Number and usually decrease the fuel consumption as well. The compositions and gasolines of the invention are unleaded and can have reduced toxicity compared to ones with aromatic amines or organo leads. In addition, contamination of the engine oil by toxic materials (e.g. lead compounds) is reduced and the fuel can be formulated to be highly immiscible with ground water.

[0110] As described above, the compound component I e.g. triptane or 2,2,3-trimethyl pentane may be used with the branched chain alkyl substituted benzene component I¹. The ratio of component I to I¹ being 0:1 to 100:1, such as 0:1 or 1:10 to 20:1 especially 5-10:1. Thus in a modification, component I¹ may be used in the substantial absence of compound I. The present invention also provides an unleaded aviation fuel composition having a MON value of at least 98, such as 99-102 and usually a final boiling point of less than 200° C. e.g. 180-190° C. and preferably an RVP at 37.8° C. of between 38-60 kPa, which comprises component a ¹which is component I¹ and component (b) as defined above, wherein 1-30% of the composition by volume is said component I¹. The present invention also provides a formulated unleaded aviation gasoline, which comprises at least one aviation gasoline additive and said aviation fuel composition. In addition the present invention also provides the use of

[0111] the compound component I¹ in unleaded aviation gasoline of MON at least 98 as an additive to or component therein to boost octane number of said gasoline. The present invention also provides a method of boosting octane number of an unleaded aviation gasoline, which comprising having said component I present in said gasoline.

[0112] The composition and formulated gasoline containing component I¹ may contain the component II, III, IV and/or an aromatic liquid hydrocarbon of 6-9 carbons, each substantially as described above.

[0113] The volume percentage of the component I¹ is usually 1-30% e.g. 5-28% such as 8-18 or 12-28%. The volume percentage of the ether may be to 30% of the total composition e.g. 1-30% such as 1-15% or 5-25%. The unleaded composition may also be substantially free of any oxygenate octane booster e.g. the ether or an alcohol. The MON level of this modified gasoline is at least 98 e.g. 98-103, 99-102 or especially 101 and the Performance Number (measured according to ASTM D909) at least for those gasolines with 15-30% component I¹ of at least 130 e.g. 130-170. Component (b) may comprise component III which has a boiling point less than 80° C., e.g. 30-60° C. below at atmospheric pressure e.g. one described above, preferably an alkane of 5 carbons e.g. isopentane, which is usually present in the composition in 0% or 1-15 such as 3-10%. This component III may be present with or substituted by an alkane of boiling point −20° to 20° C. e.g. n or isobutane in blends of 0:1 to 10:1, such as 1:3 to 3:1 or 1:2 to 2:1. The volume amount of the butane(s) in the composition is usually 1.5-10% e.g. 4-9%. The volume amount of component IV, preferably isooctane, is usually 35-80%, 45-75% such as 45-62% or 62-75%; the isooctane is preferably used substantially pure, rather than in a crude refinery fraction e.g. alkylate. Preferred blends contain butane(s): isopentane: isooctane in the volume ratios of 4-9:0-8:45-80, while preferred blends of these with tert butyl benzene are in the volume ratios 4-9:0-8:45-80:5-30. Blends of butane(s), isooctane and tert butylbenzene contain these in the volume ratio 4-9:55-75:15-30, and these blends may contain 10-20% of the ether component II.

[0114] The volume percentage of the aromatic liquid hydrocarbon (different from the branched chain component I¹) is usually 5-40% e.g. 8-35% such as 8-17% or 17-30%, with amounts of benzene less than 5% or 1% e.g. less than 0.1%. The total of the percentage of said liquid hydrocarbon and component I¹ is usually 10-35% e.g. 17-27%.

[0115] Preferred compositions and gasolines of the invention with component I¹ but without component I comprise 1.5-10% of n and/or iso butane e.g. 4-9%, 0% or 1-15% such as 3-10% component III e.g. isopentane, 35-80% e.g. 35-60 or 45-75% component IV e.g. isooctane, 5-40% e.g. 8-35 or 8-20% of one or more aromatic liquid hydrocarbons e.g. toluene and/or xylene (especially with less than 1% of benzene), 0 or 1-25% such as 5-25% of one or more asymmetric dialkylethers such as MTBE and ETBE and 1-25% such as 5-15% of component I¹ especially tertbutyl benzene. The pure aromatic hydrocarbon e.g. toluene or xylene may be replaced by a refinery fraction containing it e.g. a reformate fraction.

[0116] The physical properties of the unleaded gasolines with component I¹ are usually within the same ranges as those given above for gasolines with component I and I¹.

[0117] The unleaded gasolines with component I¹ may be converted into unleaded formulated gasolines of the invention by addition of the aviation gasoline additive as described above in the described amounts.

[0118] The gasolines of the invention may be used in internal combustion spark ignition engines. They may be used to power moving vehicles on land and/or sea and/or in the air; the invention also provides a method of moving such vehicles by combustion of a gasoline of the invention. The vehicle usually has a driver and especially means to carry at least one passenger and/or freight.

[0119] The engine sizes for motor gasoline use are usually at least 45 e.g. 45-10000 e.g. at least 200 cc, such as 500-10000 cc, in particular 950-2550, such as 950-1550, or 1250-1850 cc, or 2500-10000 such as 2500-5000 or 5000-9000 cc. The engines have at least 1 cylinders, but preferably at least 2 or 3 cylinders, e.g. 3-16, especially 4-6 or 8 cylinders; each cylinder is usually of 45-1250 cc e.g. 200-1200 cc, in particular 240-520 cc or 500-1000 cc. The engines may be 2 stroke engines, but are preferably 4 stroke ones. Rotary engines e.g. of the Wankel type may be used. The motor engines may be used to power vehicles with at least 2 wheels e.g. 2-4 powered wheels, such as motor bicycles, tricycles, and 3 wheeled cars, vans and motor cars, in particular those vehicles legislated for use on a public highway but also off road e.g. 4 wheeled drive vehicles, sports cars for highway use, and racing cars, including drag racing cars and track racing cars. Engines will preferably be connected to the wheels via a gearbox and clutch system, or drive train system, to achieve the transition from a stationary to a mobile state. The engine and drive train will best allow a range of actual vehicle road speed of between 1-350 km/h, preferably between 5-130 km/h and allow for continuous variation of speed thereof. The road speed of the vehicle is usually reduced by a braking mechanism fitted to the vehicle, the braking being generally by friction. The engine may either by air or water cooled, the air motion induced by a moving vehicle being used to directly, or indirectly cool the engine. The vehicle comprises means to facilitate a change of vehicle direction, e.g. a steering wheel or stick. Usually at least 10% of the vehicle distance travelled is carried out at greater than 5 km/h.

[0120] The engines using aviation gasoline are usually in piston driven aircraft, i.e. with at least one engine driving a means for mechanically moving air such as at least one propeller. Each engine usually drives at least one propeller driving shaft with 1 or 2 propellers. The aircraft may have 1-10 propellers e.g. 2-4. The aircraft engines usually have at least 2 cylinders, e.g. 2 to 28 cylinders, each of which is preferably greater than 700 cc in volume, such as 700-2000 cc e.g. 1310 cc. The total engine size is usually 3700-50000 cc e.g. 3700 to 12000 cc for single or twin engined passenger light aircraft, 12000 to 45000 cc for 2 or 4 engined freight or airline use (e.g. 15-200 passengers, such as 50 to 150 passengers). The engines may have an engine power to weight ratio of at least 0.3 Hp/lb wt of engine, e.g. 0.3-2 Hp/lb, and may have a power to cylinder volume of at least 0.5 (Hp/cu.in) e.g. 0.5-2. Cylinders may be arranged in rows, V formation, H formation, flat (‘horizontally opposed’) or radially around a common propeller drive shaft. One or more rows/circles of cylinders may be used, e.g. flat 2, flat 4, flat 6, V12, 2 or 3 circles of 7 cylinders etc. Every cylinder has one and more preferably at least two spark plugs. A gear system may optionally be used to drive the propeller and or a supercharger. Alternatively, an exhaust turbo charger may also be present. Exhaust outlets may be individual or run into a common manifold and preferably point in the opposite direction to forward flight. Fins may be present on the exterior of the engine for air cooling. Greater than 90% of the distance travelled by the engine, when in use, is usually spent at 500 feet or more above ground level. Typically, during greater than 90% of the time when the engine is running, the engine operates at above 1000 rpm e.g. between 1000 to 3500 rpm. The invention may be used in conjunction with a fuelling system to control at least one of the cylinder head and exhaust gas temperatures during operation by adjustment of the air: fuel ratio, e.g. reducing this reduces the temperature.

[0121] The aircraft usually has at least one tank having a capacity of at least 1001, especially with a total capacity of at least 10001. Small and micro-light aircraft may have tanks substantially smaller in capacity but can operate on the unleaded aviation gasoline described.

[0122] The gasolines of the invention may be made in a refinery by blending the ingredients to produce at least 200,0001/day of gasoline such as 1-10 million 1/day. The gasoline may be distributed to a plurality of retail outlets for motor gasoline, optionally via wholesale or bulk outlets e.g. holding tanks, such as ones of at least 2 million 1 capacity e.g. 5-15 million 1. The distribution may be by pipeline or in tanks transported by road, rail or water, the tanks being of at least 50001 capacity. At the retail sites e.g. filling station, the motor gasoline is dispensed to a plurality of users, i.e. the drivers of the vehicles, e.g. at a rate of at least 100 or 1000 different users per day. For aviation use, the gasoline is usually made in a refinery to produce at least 1000 barrels per day (or 100,0001/day) such as 0.1-2 million 1/day. The avgas is usually distributed by tanker by road, rail or water, or pipelines directly to the airport distribution or holding tanks, e.g. of at least 300,0001 capacity, from whence it is distributed by pipeline or tanker (e.g. a mobile refuelling bowser to fuel a plurality of aircraft, e.g. at least 50/day per tank; the aircraft may have one or more on-board tank each of at least 1001 capacity.

[0123] The present invention is illustrated in the following Examples.

EXAMPLES 1-6

[0124] In these Examples 2,2,3 trimethylbutane (triptane) 99% purity was mixed with various refinery fractions and butane, and optionally methyl tertiary butyl ether, to produce a series of gasoline blends, for making unleaded motor gasolines.

[0125] Formulated gasolines were made by mixing each blend with a phenolic antioxidant 55% minimum 2,4 dimethyl-6-tertiary butyl phenol 15% minimum 4 methyl-2, 6-ditertiary-butyl phenol with the remainder as a mixture of monomethyl and dimethyl-tertiary butyl phenols.

[0126] In each case the gasolines were tested for MON and RON, and their Reid Vapour Pressure at 37.8° C. and their calorific value, and their distillation properties. The results are shown in table 1. TABLE 1 Example 1 2 3 4 5 6 Composition % v/v Triptane 10.0 50.0 50.0 25.0 25.0 60.0 Butane 10.0 5.0 5.0 5.0 5.0 5.0 Mixed Fractions (apart 60.0 30.0 30.0 65.0 50.0 35.0 from Naphtha) of which Catalytic reformate 5.0 0 0 18.1 0 1.3 HCC 6.48 18.62 17.68 0 9.31 22.73 LCC 48.52 0 19.05 46.90 36.41 0.00 SRG 0 11.38 3.27 0 4.28 10.85 Isopentane 0 0 0 0 0 0.12 Naphtha 20.0 5.0 5.0 5.0 20.0 0.00 MTBE 0 10.0 0 0 0 0 Analysis, % v/v Aromatics 14.1 6.3 8.5 19.1 10.0 7.9 Olefins 23.5 3.2 11.7 21.4 18.5 3.8 Antioxidant mg/l 15 15 15 15 15 15 Distillation ° C. T 10% 43.6 58.0 58.4 51.2 54.0 60.0 T 50% 89.1 93.2 97.1 85.5 91.9 99.2 T 90% 154.0 177.8 176.9 140.4 159.0 185.0 Reid Vapour Pressure kPa 78.1 46.9 47.4 63.9 57.3 42.9 RON 95.0 97.3 97.0 97.0 95.0 99.4 MON 85.9 97.2 95.4 90.0 89.0 87.3 ROAD 90.45 97.25 96.2 93.5 92.0 93.35

[0127] In the above table mixed fractions means a blend of refinery fractions in which HCC is heavy catalytically cracked spirit, LCC is light catalytically cracked spirit and SRG is straight run gasoline.

EXAMPLE 7

[0128] The combustion characteristics of the gasolines of Ex.1-6 were tested against standard unleaded gasolines. Combustion of the gasolines of Ex. 1-6 gave less carbon dioxide emissions than from equal volumes of the standard gasolines of similar ROAD Octane Number.

EXAMPLE 8 AND COMPARATIVE Ex A-C

[0129] The emission characteristics on combustion of a series of gasoline fuels with 25% of different components were compared, the components being heavy reformate (comp A), triptane (Ex8), alkylate (comp B) and a mix of 10% heavy reformate and 15% MTBE (comp C). The gasoline fuels and their properties were as follows. Formulated gasolines were made by addition of the phenolic antioxidant in amount and nature as in Ex 1-7. Example A 8 B C Composition Butane 3 3 3 3 Reformate 22 22 22 22 Alkylate 40 40 65 40 Bisomer (‘CCS’) 10 10 10 10 Heavy Reformate 25 10 Triptane 25 MTBE 15 Density kg/l 0.7623 0.7163 0.7191 0.7424 RON 101.2 100.2 98.5 101.1 MON 89.4 93.2 88.3 90.2 ROAD 95.3 96.7 93.4 95.65 % Aromatics 38.9 13.9 13.9 23.9 % Olefins 10.2 10.2 10.2 10.2 % Saturates 50.9 75.9 75.9 65.9 % Benzene 0.9 0.9 0.9 0.9

[0130] The fuels were tested in a single cylinder research engine at a number of different engine settings. The speed/load was 20/7.2 rps/Nm/, or 50/14.3 rps/Nm the LAMBDA setting was 1.01 or 0.95, and the ignition setting was set or optimized. The emissions of CO, CO₂, total hydrocarbons, NOx, and total air toxics (benzene, butadiene, formaldehyde and acetaldehyde) were measured from the exhaust gases. The results from the different engine settings were averaged and showed that, compared to the base blend (Comp. Ex. A) the emissions with the compositions containing heavy reformate and MTBE (Comp. C), 25% alkylate (Comp. B) and 25% triptane (Ex8) were reduced, the degrees of change being as follows. TABLE 2 Example % CO % CO₂ % THC % NOx % TAT % FC Comp C (MTBE −4.9 −2.3 −6.2 −6.5 −9.2 +1.4 Comp B −7.9 −4.5 −4.0 −8.0 −13.1 −2.9 (alkylate) 8/triptane −9.6 −5.6 −6.6 −10.1 −18.7 −4.1

[0131] Where THC is total hydrocarbons, TAT is total air toxics. The Fuel Consumption (FC) was also measured in g/kWhr and the change relative to the base blend are also shown in Table 2.

EXAMPLE 9-22

[0132] Gasolines were made up as in Ex 1-6 from components as shown in the table below, and had the properties shown. They gave low carbon dioxide emissions. Example 9 10 11 12 13 14 15 Composition % v/v Triptane 10.0 25.0 60 10 18.0 10.0 24.0 Butane 4.7 4.7 4.71 0 0 0 0 Mixed Fractions (apart 85.3 70.3 35.29 76.21 73.6 90.0 45.4 from Naphtha) of which Catalytic reformate 10.0 10.0 0 21.28 10.0 15.3 25.2 CCS 0 0 0 10 0 0 0 Steam cracked spirit 0 0 0 9.7 41.1 48.7 10.0 SRG 35.3 35.3 35.29 15.72 22.5 26.0 0 Isopentane 0 0 0 0 0 0 0 Naphtha 0 0 0 13.79 8.4 0 30.6 Ethanol 0 0 0 5 0 0 0 Heavy reformate 10 10 0 9.51 0 0 0 Toluene 30 15 0 0 0 0 0 Cyclohexane 0 0 0 5 0 0 0 Light hydrocrackate 0 0 0 0 0 0 0 C6 Bisomer 0 0 0 0 0 0 10.2 Aromatics 48.0 33.0 1 31 23.6 29.2 2.2 Olefins 0.1 0.1 0.1 6.1 8.8 10.4 12.5 Sulphur % w/w 0.000 0.000 0.002 0.001 0.004 Benzene 0.7 0.7 0.6 0.9 1.0 Antioxidant mg/l 15 15 15 15 15 15 15 Distillation ° C. T 10% 58.0 55.9 53.6 51.5 61.0 T 50% 95.9 89.9 77.0 77.0 89.6 T 90% 156.6 157.0 136.9 142.6 140.4 Reid Vap. Pres. kPa 51.6 54.0 56.9 60.0 50.0 RON 97.3 96.1 101.4 96.0 91.0 92.0 91.0 MON 88.1 87.8 88.8 83.8 81.6 81.8 82.0 ROAD 92.7 91.9 95.1 89.9 86.3 86.9 86.5 Example 16 17 18 19 20 21 22 23 Composition % v/v Triptane 10 25 60 10 25.0 25.0 25.0 25.0** Butane 2.96 2.96 2.96 0 3.32 1.07 3 Mixed Fractions 87.04 72.04 37.04 76.21 54.95 65.42 75.0 (apart from Naphtha) Catalytic reformate* 19.78 4.78 21.28 23.42 8.21 7.53 40 CCS 5 5 5 10 Steam cracked spirit* 47.42 47.42 18.0 9.7 30.01 30.00 SRG 15.72 Alkylate 31.53 27.20 37.47 22 Naphtha 13.79 16.73 8.51 Ethanol 5 Heavy reformate 9.51 Cyclohexane 5 5 5 5 Light hydrocrackate 7.93 7.93 7.93 0 C6 Bisomer 1.91 1.91 1.91 0 10 Analysis, % v/v Aromatics 32.1 23 8 31 16.4 16.8 15.6 25.5 Olefins 14 13.9 7.3 6.1 0.2 7.8 7.8 10.2 Benzene 1.0 0.5 0.5 1.71 Sulphur % w/w 0.0002 0.0004 0.0004 0.0001 Antioxidant mg/l 10 10 10 10 10 10 10 10 Distillation % 70° C. 22.7 31.2 30.5 18.5 % 100° C. 53.3 60.0 59.2 42.5 % 150° C. 95.8 94.9 95.1 97.2 % 180° C. 98.7 98.1 98.1 100 Reid Vap. Press. kPa 60.0 55.0 52.7 62.2 RON 97.3 98.9 104.0 96.0 98.6 100.9 102.9 102.7 MON 85.5 87.2 93.4 83.8 87.5 87.5 89.5 90.5 ROAD 91.4 93.05 96.7 89.8 93.05 94.2 96.2 96.6

EXAMPLES 24-8 AND COMPARATIVE EXAMPLE D

[0133] Emission characteristics were obtained as in Ex.8 (apart from Lamba settings of 1.00 and 0.95 set for the base fuel (Comp.D) on combustion of a series of gasoline fuels with different components namely reformate, (high aromatics), (Comp.D), triptane, Ex.24-27 and triptane/ethanol Ex.28. Fuel consumption was also measured in g/kWhr. Formulated gasolines were made by addition of the phenolic antioxidant in amount and nature as in Ex. 1-7. The compositions were as shown in Table 3. The results were expressed in Table 4 as the percentage change in emissions or in fuel consumption compared to Ex.D. TABLE 3 Example 24 25 26 27 28 D Composition % v/v Triptane 40 10 25 60 10 Butane 2.96 2.96 2.96 2.96 2.96 Mixed Fractions (apart from 87.04 72.04 37.04 Naphtha) of which Catalytic reformate* 19.78 4.78 21.28 25.25 CCS 5 5 5 5 10 5 Steam cracked spirit* 37.2 47.42 47.42 17.2 9.7 47.42 SRG 15.72 Toluene 4.53 Naphtha 13.79 Ethanol 5 Heavy reformate 9.51 Cyclohexane 5 5 5 5 5 5 Light hydrocrackate* 7.93 7.93 7.93 7.93 7.93 C6 Bisomer* 1.91 1.91 1.91 1.91 1.91 Analysis, % v/v Aromatics 15.0 31.2 21,7 7.8 31.1 39.2 Olefins 13.4 16.2 16.1 8.3 6.5 16.2 Sulphur % w/w 0.007 0.007 0.007 0.007 0.012 0.007 Antioxidant mg/l 10 10 10 10 10 10 Distillation ° C. % T 10% T 50% T 90% Reid Vapour Pressure kPa RON 98.7 96.8 97.5 101.0 93.2 96.6 MON 86.1 82.8 83.7 89.6 82.4 82.5 ROAD 92.4 89.8 90.6 95.3 88.1 89.55

[0134] TABLE 4 % Fuel Example % CO % CO2 % THC % NOx % TAT Consumption 25 −3.3 −2.1 −4.7 −4.0 −5.0 −1.4 26 −8.6 −3.8 −8.7 −7.0 −19.1 −2.5 27 −17.4 −6.8 −10.5 −18.0 −35.3 −4.5 24 −14.9 −5.0 −7.9 −12.2 −28.7 −3.4 28 −11.7 −2.2 −3.2 −10.3 −10.1 +0.1

[0135] TABLE 5 Example F.G 29 Composition % v/v Triptane 25 Butane 0.75 0 Mixed Fractions (apart from Naphtha) of which Catalytic reformate* 11.0 7.5 Steam cracked spirit* 31.5 30.0 Alkylate 40.9 37.5 Toluene 15.8 0 Analysis, % v/v Aromatics 34.2 15.6 Olefins 8.2 7.8 Saturates 57.6 76.6 Sulphur ppm 7.3 10 Benzene % w/w 0.75 0.64 Antioxidant mg/l 10 10 Distillation % Evap. 70° C. 18.8 21.6 E % 100° C. 44.4 64.5 E % 150° C. 92.8 93.3 E % 180° C. 96.4 98 Reid Vapour Pressure kPa 56.8 52.2 RON 99.5 99.7 MON 87.6 89.3 ROAD 93.05 94.5

EXAMPLES 29 AND COMPARATIVE EX. F, G

[0136] 3 gasoline fuels (Ex.29, F and G) were compared for production of emissions on combustion in cars. The gasoline fuels had the compositions and properties as shown in Table 5 and the formulated gasolines included antioxidant as in Ex. 1. The fuels met the requirements of 2005 Clean Fuel specification according to Directive 98/70 EC Annexe 3. The cars were regular production models, namely 1998 Ford Focus (1800 cc), 1996-7 VW Golf (1600 cc), 1998 Vauxhall Corsa (1000 cc), 1994-5 Peugeot 106 (1400 cc) and 1998 Mitsubishi GDI (1800 cc) each fitted with a catalytic converter. The Corsa had 3 cylinders, the rest 4 cylinders, while the 106 had single point injection the Mitsubishi had direct injection and the rest multipoint injection for their combustion.

[0137] 2 separate base fuel experiments (comp F & G) were done. The emissions were tested in triplicate in a dynamometer on the European Drive Cycle test as described in the MVEG test cycle (EC.15.04+EUDC) modified to start sampling on cranking and 11 sec. Idle as given in Directive 98/69 EC (the disclosure of which is hereby incorporated by reference). The EDC test over 11 km comprises the ECE cycle (City driving test) repeated 4 times followed by the Extended Urban Drive Cycle test (incorporating some driving at up to 120 km/hr). The emissions were measured out of the engine (i.e. upstream of the catalytic converter) and also as tailpipe emissions (i.e. downstream of the converter) and were sampled every second (except for the Focus) and cumulated over the test, the results being expressed as g emission per km travelled. The emissions of the first ECE cycle with the Focus were not measured. The emissions tested were for the total hydrocarbons, CO₂, CO and NOx and the fuel consumption was determined on a gravimetric basis. The geometric means of the emission and consumption results across the 5 cars were obtained. The values for the Comparative fuels were averaged.

[0138] In the following tests, the CO₂ emissions averaged over the 5 cars were lower with the triptane fuel (Ex.29) compared to the averaged base fuel results (Comp.F, G), namely Total tailpipe emissions in EDC tests, EUDC test and ECE test, the reductions being respectively 2.8%, 2.7% and 2.8%. The Fuel Consumptions averaged over the 5 cars were lower with the triptane fuel (Ex.29) compared to the averaged base results (Comp.F, G) in those same tests, the reductions being respectively, 0.6%, 0.6% and 0.5%. The tailpipe emissions results for THC, CO and NOx in at least some parts of the total EDC cycle showed trends towards triptane giving lower emissions than the base fuel, but the differences may or may not be confirmed in view of the limited number of vehicles tested.

[0139] The ECE tests simulates city driving and has 4 identical repeats of a specified speed profile, which profile has 3 progressively higher speed sections interspersed by zero speed sections (the average speed being 19 km/hr). The first profile corresponds to driving from a cold start. In a cold engine, the effects of friction, lubricants and the nature of the fuel among others, differ from those with a hot engine in an unpredictable way, and it is with cold engines that most tailpipe emissions are produced, because the catalytic converter becomes increasingly effective at reducing emissions when it becomes hot. In addition a Lambda sensor upstream of the converter controls the fuel/air ratio entering the engine, but this is not effective with a cold engine (resulting in an unregulated fuel/air ratio); after cold start the sensor quickly becomes effective, (resulting in a regulated fuel/air ratio), even when the catalyst is not yet hot enough to be effective. Thus cold start operations are different from hot running operations and yet contribute to a large amount of tailpipe emissions.

[0140] The out of engine results from the first profile ECE tests (simulating cold start) with the above fuels (Ex.29 and Comp.F, G) were the same as the tailpipe emissions as the catalyst was not effective then. The results in these cold start tests for CO₂, HC, CO and NOx averaged over the Golf, Corsa, Peugeot and Mitsubishi, and also averaged over the Golf, Corsa and Peugeot showed trends toward triptane giving lower emissions than the base fuel, but the differences may or may not be confirmed in view of the limited number of vehicles tested.

[0141] This period of cold start simulated as above may correspond in real life to a period of time or distance, which may vary, depending on how the car is driven and/or ambient conditions e.g. up to 1 km or 4 or 2 min, or a temperature of the engine coolant (e.g. radiator water temperature) of up to 50° C. The car engine may also be deemed cold if it has not been operated for the previous 4 hr before start, usually at least 6 hr before start.

[0142] Thus the present invention also provides of method of reducing emissions of exhaust gases in the combustion of unleaded gasoline fuels of MON of at least 80 e.g. 80 to less than 98 from cold start of a spark ignition combustion engine, which comprises having a compound of formula I present in the fuel which is a gasoline of the invention.

EXAMPLE 30

[0143] An unleaded aviation gasoline was made by mixing 2,2,3 trimethylbutane of 99% purity with iso-pentane and iso-octane to give a composition consisting of 2,2,3 trimethylbutane 40%, isopentane 12%, and iso-octane 48% expressed in volume percentages of the total gasoline.

[0144] The motor octane number (MON) of the gasoline was 99.9 as determined by ASTM D2700-92 and the Reid Vapour Pressure was 33 kPa.

EXAMPLE 31

[0145] An unleaded aviation gasoline contained the gasoline of Ex.30 with 8 mg/l of a mixture of 75% 2,6-ditertiary, butyl phenol and 25% tertiary and tri tertiary, butyl phenols, as antioxidant.

EXAMPLE 32

[0146] An unleaded aviation gasoline was made from a crude triptane fraction. A cracked residue from the distillation of crude oil was distilled to give a C₄ fraction containing olefin and saturates. The fraction was alkylated (i.e. self reacted) to form a crude C₈ saturate which was distilled to give a fraction boiling 95-120° C., which contained 223 and 233 trimethyl pentane. This fraction was demethylated by reduction to give a first fraction containing about 17% triptane and 83% iso C₆-C₉ with a majority of iso C₇ and iso C₈ hydrocarbons. This first fraction was redistilled to produce a second fraction of 87% triptane and 13% iso C₇ and C₈.

[0147] 90 parts by volume of this second fraction was mixed with 10 parts of isopentane to give an unleaded aviation gasoline of MON value 99.1. Addition of 8 mg/l of the phenol mixture of Ex.31 gave an oxidation stabilized unleaded aviation gasoline fuel.

EXAMPLE 33

[0148] The process of Example 32 was repeated with the first fraction containing the 17% triptane redistilled to give a third fraction containing 37% triptane and 63% iso C₇ and C₈. 82 parts by volume of this third fraction were mixed with 18 parts of isopentane to give an unleaded aviation gasoline of MON value 98.0. Addition of the phenol mixture as in Ex.32 gave an oxidation stabilised aviation gasoline fuel.

EXAMPLES 34-38

[0149] In these Examples 2,2,3 trimethylbutane (triptane) 99% purity was mixed with isopentane and butane, and optionally toluene and/or methyl tertiary butyl ether, to produce a series of gasoline blends, for making unleaded aviation gasolines.

[0150] The formulated gasolines were made by mixing each blend with a phenolic antioxidant (as described in Ex. 1-6) (DEF STAN 91-90 RDE/A/610).

[0151] In each case the gasolines were tested for Motor Octane Number, and their Reid Vapour Pressure at 37.8° C. and their calorific value, and their distillation properties and freezing point. In addition for Example 38 the Indicated Mean Effective Pressure (IMEP) was determined (according to ASTM D909) to give the Supercharge Performance Number. The results are shown in Table 6. TABLE 6 Example 34 35 36 37 38 Composition % v/v Triptane 85.0 73.0 53.0 87.8 87.0 Isopentane 12.0 14.0 14.0 12.0 11.8 Butane 3.0 3.0 3.0 0.2 1.2 Toluene — 10.0 10.0 — — MTBE — — 20.0 — — Antioxidant mg/l 15 15 24 17 15 Distillation ° C. Initial Boiling Point 43.0 41.0 36.5 47.5 46.5 T 10% 63.5 63.5 57.0 68.0 67.0 T 40% 77.0 79.0 69.9 76.5 77.0 T 50% 78.5 81.5 73.8 78.5 79.0 T 90% 80.5 87.5 88.4 80.5 81.0 Final Boiling Point 115.0 116.0 107.7 80.5 90.0 Reid Vapour Pressure kPa 51.3 52.5 58.3 40.4 46.3 MON 99.8 98.3 98.0 99.7 99.8 Freezing point ° C. −54 <−80 <−80 −49 −51.5 Supercharge (IMEP) — — — — >160 Specific energy MJ/kg 44.5 44.1 42.1 44.5 44.5

EXAMPLES 39-41 AND COMPARATIVE EX. H, J

[0152] Blends for use in making unleaded aviation gasolines were made with the composition as shown in Table 7 below in which Ex.39 and 40 are repeats of Ex.9 and 1 respectively. To make the formulated unleaded aviation gasolines, the blends were mixed in the amounts of the antioxidant, as described in Ex. 1-6 above. The gasolines were compared with commercial UK market leaded aviation gasolines (Comp. Ex. H and J) All the gasolines met Def.Standard 91-90. Composition Comp. H Ex. 39 Comp. J Ex. 40 Ex. 41 Triptane % v/v 87.0 40.0 60.0 Isopentane % v/v 11.8 12.0 Iso-octane % v/v 48.0 Alkylate 95 to 125° C. 28.0 cut Isomerate % v/v 12.0 Butane 1.2 Anti-oxidant mg/l 15 9 17 Distillation IBP ° C. 33.5 46.5 37.5 — 54.2 T 10% Evap. ° C. 64.3 67.0 63.5 — 74.9 T 40% Evap. ° C. 97.6 77.0 98.0 — 83.4 T 50% Evap. ° C. 103.4 79.0 102.5 — 85.2 T 90% Evap. ° C. 120.8 81.0 119.0 — 97.0 FBP ° C. 150.7 90.0 150.0 — 114.7 Temp. E10% + E50% 167.7 146.0 166.0 — 160.1 RVP kPa 45.1 46.3 47.6 33.0 32.9 Calorific value MJ/kg 44.117 44.493 43.711 44.442 44.429 Lead gPb/l 0.51 0.00 0.48 0.00 0.00> MON ON 102 99 101 99 98

[0153] The emission characteristics of the gasolines were compared. The gasolines were tested in a single cylinder research engine at a number of settings and under conditions corresponding to take off full power (42 rps/36 Nm at Lambda 0.85) and cruise 42 rps/22 Nm at Lambda 1.15 with optimised ignition settings. The emissions of THC (total hydrocarbons), CO, NO_(x), CO₂ were measured on the exhaust gases, and also the fuel consumption (FC) expressed in g/kWhr. Tables 8 and 9 below show the changes in levels with the gasolines of the invention compared to the commercial aviation gasoline, Ex.39 being compared to Comp. Ex. H in Table 8, and Ex. 40 and 41 being compared to Comp. Ex. J in Table 9. The tests for Table 9 were done in triplicate and the results averaged. TABLE 8 Change for Ex. 39 compared to base gasoline (Comp. H) Conditions CO₂ % CO % THC % No_(x) % FC % Take off −7.2 −4.0 −15.6 −11.2 −5.2 Cruise −2.6 −0.9 −14.0 −4.2 −1.4

[0154] TABLE 9 Change for Ex. 40 and 41 compared to gasoline Comp. J. Conditions CO₂ % CO % THC % No_(x) % FC % Take off Ex. 40 −4.2 −1.8 −4.8 −8.7 −1.8 Ex. 41 −3.3 −3.9 −6.8 −5.1 −1.8 Cruise Ex. 40 −3.8 1.0 −5.8 −17.2 −2.1 Ex. 41 −4.1 0.4 −8.1 −12.1 −2.3

[0155] The results in Tables 8 and 9 show the reduction in emissions of THC, CO₂, NO_(x), and Fuel Consumption, for the aviation gasolines of the invention compared to the commercial leaded aviation gasolines.

EXAMPLE 42

[0156] An unleaded aviation gasoline blend was made by mixing 55% by volume of 223 trimethyl butane of 99% purity with 10% by volume of isomerate, (containing 54.8% isopentane 14.1% 2,2 dimethylbutane, 19.1% of 2 and 3 methylpentanes and the remainder other hydrocarbons of 5-10 carbons), 3% of volume of butane, 20% of isooctane (224 trimethyl pentane) and 12% of an alkylate fraction (bp 90-135° C. containing 51% isooctane, 21% other trimethyl pentanes and 22% mixed isomeric hydrocarbons.

[0157] The MON of the gasoline was 99.3 as determined by ASTMD 2700-92, the Reid Vapour Pressure was 40.9 kPa, the Supercharge Performance Number greater than 133 (determined from the Indicated Mean Effective Pressure IMEP/reference fuels—see ASTM D909), and the freezing point less than −80° C.

[0158] A formulated unleaded aviation gasoline contained the above gasoline blend and 15 mg/l of a phenol antioxidant 55% minimum 2,4 dimethyl-6-tertiary butyl phenol 15% minimum 4 methyl-2,6-ditertiary-butyl phenol with the remainder as a mixture of monomethyl and dimethyl-tertiary butyl phenols (DEF STAN 91-90 RDE/A/610). The gasoline analysis is given in Table 10.

[0159] The gasoline was also tested for carbon dioxide, carbon monoxide. No_(x) and total hydrocarbon emissions against a standard leaded aviation gasoline in a research engine operating at 42 rps/20.5 Nm and Lambda 1.15 (representing aircraft cruise conditions) with the ignition setting optimised for the standard gasoline. The emissions were reduced, the changes being —4.1% CO₂, −1.1% CO, −3.9% CO_(x), −8.7% NO_(x), −6.2% THC.

[0160] The exhaust gas temperatures were an average of 617° C. for the standard leaded fuel and 609° C. for the gasoline of the invention. TABLE 10 Antioxidant mg/l 15 Visual appearance Pass Density @ 15 Deg C. kg/l 0.6914 Distillation IBP Deg C. 41.0 T10% Deg C. 71.8 T40% Deg C. 83.9 T50% Deg C. 85.6 T90% Deg C. 94.9 FBP Deg C. 112.0 Temp E10% + E50% Deg C. 157.0 Recovery % v/v 97.6 Residue % v/v 0.9 Loss % v/v 1.5 RVP kPa 40.9 Freezing point Deg C. <−80 Sulphur % w/w <0.01 Copper corrosion 2h 100 Deg C. 1A Oxidation stability 16h Potential gum mg/100 ml 7 Lead precipitate mg/100 ml 0 Volume change 0 Carbon:Hydrogen Ratio 1:2.288 Specific energy MJ/kg 44.431 Octane MON 99.3 Super charge PN >133

EXAMPLES 43-57

[0161] Unleaded aviation gasoline blends 1-15 were made by mixing the ingredients shown in Table 12.

[0162] A corresponding series of formulated unleaded aviation gasolines contained the individual blends and 10 mg/l of the phenol antioxidant used in Example 42. The gasolines are tested for emissions on combustion and give reduced emissions compared to the standard leaded gasoline as in Ex.42.

[0163] In the Table cut alkylate is an alkylate fraction boiling at 95-105° C. containing a majority of isooctane and also 7-10 carbon alkanes, cut reformate is a reformate fraction boiling at 105-135° C. and consisting of aromatics, in particular toluene and xylene and isomerate contains a majority of isopentane and also other 4-10 carbon alkanes. The physical properties of the cut alkylate cut reformate and isomerate are given in Table 11. TABLE 11 COMPONENT Cut alkylate Cut reformate 105 DATA 95-105 C. to 135 C. Isomerate MON 96 99.3 87.2 RVP kPa 14.1 8.5 94.2 IBP° C. 90.6 103.2 31.8 FBP 124.9 153.6 83.6 E75° C. 0 0 97.7 E105° C. 80 2.1 99.3 E135° C. 99 91.6 99.3

[0164] TABLE 12 Blend 1 Blend 2 Blend 3 Blend 4 Blend 5 Blend 6 Blend 7 BLENDS % v/v % v/v % v/v % v/v % v/v % v/v % v/v Cut alkylate 4 9 Cut reformate 5 9.2 10 7 Isomerate 7.13 5 6 8 Triptane 80 89.84 73.42 85 75 80 80 Isopentane 15 17.38 15 Butane 3.03 6 5 5 Iso-octane Anti-oxidant mg/l 10 10 10 10 10 10 10 Properties MON 99.8 100 99.5 99.9 99.5 99.4 99.5 Supercharge >130 >130 >130 >130 >130 >130 >130 RVP kPa 36.4 38 38 37.1 44.4 42.8 44 E75 C % v/v 15 10 17.4 15 10.9 10.9 12.8 E105 C % v/v 95.1 100 91 100 89.4 98.2 93.1 E135 C % v/v 99.6 100 99.2 100 99.1 99.9 99.4 Density kg/l 0.7008 0.6861 0.7077 0.6926 0.7006 0.685 0.695 Benzene % v/v 0.01 0 0.02 0 0.02 0 0.01 Blend Blend blend blend Blend Blend Blend Blend 8 9 10 11 12 13 14 15 BLENDS % v/v % v/v % v/v % v/v % v/v % v/v % v/v % v/v Cut alkylate 2.82 10 10 17 Cut reformate 7.04 7.71 10 5 5 Isomerate 6 9.71 9.29 Triptane 80 80 80 75 75 65 80 70 Isopentane 10 10 15 13 10 Butane 4.13 3 3 5 5 5 2 3 Iso-octane 7.29 Anti-oxidant 10 10 10 10 10 10 10 10 mg/l Properties MON 99.7 99.5 99.5 99.6 99.3 98.7 99.8 99.9 Supercharge >130 >130 >130 >130 >130 >130 >130 >130 RVP kPa 39.5 38.6 38.3 47.3 47.9 51.8 41 40.0 E75 C % v/v 10 12.5 12.1 15 15 20 15 12.8 E105 C % v/v 92.5 99.9 92.4 90.2 98 93.1 95.1 97.0 E135 C % v/v 99.3 99.9 99.3 99.2 99.9 99.5 99.6 99.9 Density kg/l 0.6972 0.6852 0.6978 0.7035 0.6877 0.6958 0.6986 0.695 Benzene % v/v 0.01 0 0.01 0.02 0 0.01 0.01 0

EXAMPLES 58-69

[0165] Unleaded aviation gasoline blends 1-11 were made by mixing the ingredients shown in Tables 13 and 14 and had properties as shown in the Tables; all were essentially free of benzene (<0.1% w/w). A corresponding series of formulated unleaded aviation gasolines containing the blends and 10 mg/l of the phenol antioxidant of Ex.42 were made. The gasolines are tested for emissions on combustion and give reduced emissions compared to the standard leaded avgas used in Example 42. TABLE 13 Blend 1 Blend 2 Blend 3 Blend 4 Blend 5 Density kg/l 0.7186 0.7144 0.7039 0.711 0.7495 RVP kPa 47.6 45.6 44.2 43.9 42.5 Initial boiling Deg C. 37.8 39.5 40.5 38.1 38 point T10% Deg C. 72.2 71.2 74.7 71.6 84.3 T40% Deg C. 83.6 84.5 83.8 82.6 101.8 T50% Deg C. 84.5 86.3 84.4 83.7 102.8 T90% Deg C. 124.5 121.1 123.0 125.6 124.1 T10% + T50% Deg C. 156.7 157.5 159.1 155.3 187.1 Final boiling Deg C. 180.2 181 185.1 181.1 184.9 point Loss % v/v 1.4 0.7 1.7 1.8 1.3 Residue % v/v 0.6 0.6 0.6 0.6 0.7 MON ON 100.6 100.2 101.3 100.7 98.1 Freeze Point Deg C. <−60 <−60 <−60 C4 butanes % v/v 5 4 5 5 5 Isopentane % v/v 2 5 5 2,2,3-Tri- % v/v 76 65 79 60 methylbutane (triptane) 2,2,4-Tri- % v/v 11 2 5 55 methylpentane Toluene % v/v 7 5 4 5 25 ETBE 15 tert-butyl- % v/v 10 10 10 10 10 benzene

[0166] TABLE 14 Blend Blend Blend 6 Blend 7 Blend 8 Blend 9 10 11 Tert- % v/v 25 15 15 20 10 10 butyl- benzene Butanes % v/v 7 6 6 6 6 6 Iso- % v/v 5 5 5 pentane Iso- % v/v 68 64 64 69 69 50 octanes Toluene % v/v 5 5 Xylenes % v/v 5 10 MTBE % v/v 15 ETBE % v/v 15 14 MON 101.4 101 101 100.6 99.8 99.9 RVP kPa 43 48 42 45 46 48 Density kg/l 0.7287 0.7196 0.7213 0.7178 0.7177 0.7344 Freeze Deg <−60 <−60 <−60 <−60 <−60 <−60 point C. Ben- % <1.0 <1.0 <1.0 <1.0 <1.0 <1.0 zene w/w Anti- mg/l 10 10 10 10 10 10 oxidant 

We claim:
 1. An unleaded formulated gasoline comprising a base blend composition having a Motor Octane Number (MON) of at least 80 comprising component (a) at least 5% (by volume of the total composition) of at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 12 carbon atoms, and at least one gasoline additive.
 2. An unleaded formulated motor gasoline according to claim 1 which comprises at least one motor gasoline additive.
 3. A gasoline according to claim 1 wherein said composition has a MON value of 80 to less than 98 and said saturated hydrocarbon has 4 to 10 carbons.
 4. A gasoline according to claim 2 which comprises as component (a) at least 8% of triptane and said saturated hydrocarbon has 5 to 10 carbon atoms.
 5. An unleaded formulated gasoline comprising a base blend composition having a Motor Octane Number (MON) of at least 80 comprising component (a) at least 5% (by volume of the total composition) of at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I wherein R is hydrogen or methyl and as component (b) at least one of isomerate, alkylate, straight run gasoline, and light hydrocrackate, and at least one motor gasoline additive.
 6. A gasoline according to claim 5 wherein said composition has a MON value of 80 to less than
 98. 7. A gasoline according to claim 6 wherein said composition comprises at least 8% of triptane and wherein component b comprises at least one of isomerate, alkylate, aviation alkylate and straight run gasoline and comprises at least one saturated liquid aliphatic hydrocarbon having 5-10 carbon atoms.
 8. A gasoline according to claim 1 which comprises at least one saturated aliphatic hydrocarbon having 4-6 carbons, which has a lower boiling point than triptane and has a Motor Octane Number greater than
 88. 9. A gasoline according to claim 1 which comprises at least one saturated aliphatic hydrocarbon having 5-10 carbon atoms, which has a higher boiling point than triptane and has a Motor Octane Number greater than
 92. 10. A gasoline according to claim 2 which comprises at least one olefin which is an alkene of 5-10 carbons, with a MON value of 70-90 in amount of 1-30%, preferably 5-20%.
 11. A gasoline according to claim 10 which comprises at least one of catalytically cracked spirit, steam cracked spirit C₆ bisomer, catalytic polymerate and dimate.
 12. A gasoline according to claim 11 which comprises catalytically cracked spirit.
 13. A gasoline according to claim 1 which also comprises at least one aromatic compound of MON value 90-110, in amount of 2-40% especially 3-28% (by volume).
 14. A gasoline according to claim 13 which also comprises catalytically reformed or cracked gasoline.
 15. A gasoline according to claim 1 which also comprises at least one oxygenate octane booster of MON value of at least 96 in amount of 1-25%.
 16. A gasoline according to claim 2 which has a Reid Vapour pressure at 37.8° C. measured according to ASTM D323 of 40-100 kPa.
 17. A gasoline according to claim 2 which meets the following criterion ${{{Atom}\quad H\text{:}C \times \left\lbrack {1 + {oxy}} \right\rbrack \times \left\lbrack {\frac{{Net}\quad {Heat}\quad {of}\quad {Combustion}}{200} + {ROAD}} \right\rbrack} \geq y},$

wherein Atom H:C is the fraction of hydrogen to carbon in the hydrocarbons in the composition, oxy means the molar fraction of oxygenate, if any, in the composition, Net Heat of Combustion is the energy derived from burning 1 lb (454 g) weight of fuel (in gaseous form) in oxygen to give gaseous water and carbon dioxide expressed in Btu/lb units [MJ/kg times 430.35], and y is at least 350 in particular 350-440, and ROAD is the average of Motor Octane Number and Research Octane Number.
 18. A gasoline according to claim 2 which comprises 10-90% of triptane, 10-80% of component (b), 0-25% naphtha, 0-15% of butane, 0-20% of olefin, 3-28% aromatics and 0-25% oxygenate.
 19. A gasoline according to claim 2 which comprises 5-20% aromatics, and 5-18.5% olefins.
 20. A gasoline according to claim 2, which comprises 8-65% of triptane, especially 15-35%, 0.1-30% such as 2-25% olefins, especially 3-14% and 5-35% aromatics, 5-50% component (b) mixtures, oxygenates, in amount of less than 3% and less than 1.5% benzene e.g. 0.1-1%, and having RON of 97-99, MON 87-90 and ROAD values of 92-94.5.
 21. A gasoline according to claim 2, which comprises 5-25% triptane, 5-15% olefins, 15-35% aromatics and 40-65% component (b) and of RON value 94.5-97.5, in particular 15-25% triptane, 7-15% olefins, 15-25% aromatics and 45-52% component (b) mixture and of RON value 96.5-97.5.
 22. A gasoline according to claim 2, which comprises 1-15%, butane, 0-20% MTBE, 20-80% of refinery mixed liquid C₆-C₉ streams (apart from naphtha) 0-25% naphtha, 15-65% triptane, with RON 93-100, MON 80-98, and RVP 40-80 kPa, with 1-30% olefins and 2-30% aromatics.
 23. A gasoline according to claim 2 which comprises 8-18% triptane, 10-50% e.g. 25-40% of total component (b) mixture, 5-40% e.g. 20-35% of total aromatics mixture, 15-30% of total olefinic mixture and 0-15% total oxygenate.
 24. A gasoline according to claim 2 which comprises 20-40% triptane, 8-55% of the total component (b) mixture, 5-25% total aromatics mixture, and 10-55% total olefin mixture.
 25. A gasoline according to claim 2 which comprises 40-55% triptane, 5-30% total component (b) mixture, 0-10% total aromatic mixture, 10-45% olefinic mixture and 0-15% oxygenates, with the total of oxygenates (if any) and olefinic mixture of 20-45%.
 26. A gasoline according to claim 2 which comprises 55-70% triptane, 10-45% total component b, and 0-10% total aromatics Mixture, and 0-30% total olefinics mixtures, especially 55-70% triptane, 10-25% total component (b), 0 or 0.5-5% total aromatics mixture and 15-30% total olefinic mixture.
 27. A gasoline according to claim 2 which has a ROAD Index, which is the average of MON and RON, of 85.5-88.5, and comprises 8-30% triptane and 10-50% total component (b) mixture, 5-30% total olefins and 10-40% total aromatics.
 28. A gasoline according to claim 2 which has a ROAD Index of 88.5-91.0 and comprises 5-25% triptane, 20-45% total component (b) mixture, 1-25% total olefins, and 10-35% e.g. 10-20% or 20-35% total aromatics.
 29. A gasoline according to claim 2 which has a ROAD Index of 91.0-94.0, and comprises 5-65% triptane and 5-40% total component (b) mixture, 1-30% total olefins and 5-55% total aromatics.
 30. A gasoline according to claim 2 which has a ROAD Index of 94-97.9, and comprises 20-65% triptane, 5-15% total olefins, 5-20% total aromatics and 5-50% total component (b) mixture.
 31. A gasoline according to claim 2 which comprises 15-35% triptane, 0-18.5% olefin, 5-40% aromatics and 25-65% saturates and has less than 1% benzene.
 32. A gasoline according to claim 2 which comprises 40-65% triptane, 5-18.5% olefins, 5-28% aromatics and 35-55% saturates and less than 1% benzene.
 33. A gasoline according to claim 2 wherein motor gasoline additive is an antioxidant, corrosion inhibitor, anti-icing additive, engine detergent additive or anti-static additive, or mixture thereof.
 34. A gasoline according to claim 5 wherein the motor gasoline additive is an antioxidant, corrosion inhibitor, anti-icing additive, engine detergent additive or anti-static additive, or mixture thereof.
 35. A gasoline according to claim 33 wherein the additive is an antioxidant.
 36. An unleaded aviation fuel, having a Motor Octane Number of at least 98, and having a final boiling point of less than 170° C. which comprises: component (a) comprising at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  (I) wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 5 or 6 carbon atoms wherein at least 20% by volume of the total composition is a hydrocarbon of formula I, together with at least one aviation gasoline additive.
 37. A fuel according to claim 36 wherein the hydrocarbon of formula I is triptane.
 38. A fuel according to claim 37 having a Reid Vapour Pressure at 37.8° C. of 38-60 kPascals.
 39. A fuel according to claim 38 with a Reid Vapour Pressure of 38-49 kpascals.
 40. A fuel according to claim 37 wherein component (b) comprises a component (III) which is more volatile and has a lower boiling point than triptane, and has a Motor Octane Number greater than
 88. 41. A fuel according to claim 40 wherein component (III) comprises iso-pentane.
 42. A fuel according to claim 41 wherein the fuel composition comprises 5-40% by volume of iso-pentane.
 43. A fuel according to claim 41 wherein component (III) comprises butane and iso-pentane.
 44. A fuel according to claim 40 wherein the fuel composition comprises 0.1-3.0% by volume of n-butane.
 45. A fuel according to claim 40 wherein component (b) comprises in addition to component (III) a component (IV) having a boiling point higher than triptane but less than 170° C. and having a Motor Octane Number of at least
 92. 46. A fuel according to claim 45 wherein component (IV) is iso-octane.
 47. A fuel according to claim 36 wherein the composition comprises up to 30% by volume of an aromatic liquid hydrocarbon of 6-8 carbons.
 48. A fuel according to claim 47 wherein the composition comprises 5-30% by volume of toluene.
 49. A fuel according to claim 36 which comprises as component (I) said hydrocarbon having the formula I and a component (II) an oxygenate octane booster.
 50. A fuel according to claim 49 wherein the component (II) is an ether.
 51. A fuel according to claim 50 wherein the ether is methyl tertiary butyl ether.
 52. A fuel according to claim 36 wherein 35-92% by volume of the total composition is the combined volume of the hydrocarbon of formula I and methyl tertiary butyl ether (if present).
 53. A fuel according to claim 41 which comprises 80-90% of triptane, with isopentane and optionally butane.
 54. A fuel according to claim 41 which comprises 30-80% of triptane, and also III isopentane and IV iso-octane, the volume ratio of III to IV being 35-15:65-85.
 55. A fuel according to claim 48 which comprises 50-90% triptane, 5-25% isopentane and 5-30% toluene.
 56. A fuel according to claim 55 which comprises 0-15% methyl tertiary butyl ether.
 57. A fuel according to claim 36 which has a calorific value of at least 42 MJ/kg.
 58. A fuel according to claim 57 which has a calorific value of at least 43.5 MJ/kg.
 59. A fuel according to claim 36 wherein the Performance Number for supercharging is at least
 130. 60. An fuel according to claim 36 wherein the aviation gasoline additive is selected from anti-oxidants, corrosion inhibitors, anti-icing additives and anti-static additives.
 61. A fuel according to claim 60 wherein the antioxidant is one or more hindered phenols.
 62. An unleaded blend composition having a Motor Octane Number (MON) of at least 80 comprising component (a) at least 5% (by volume of the total composition) of at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 12 carbon atoms, and also either comprises at least one of an olefin of 5-10 carbon atoms, aromatic compound in amount of 1-28% or benzene in amount of less than 5% benzene, or comprises at least 20% of said compound of formula 1, has a MON of at least 98 and has a final boiling point of less than 170° C.
 63. An unleaded blend composition having a Motor Octane Number (MON) of at least 80 comprising component (a) at least 5% (by volume of the total composition) of at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 12 carbon atoms, and also comprises at least one of an olefin of 5-10 carbon atoms, aromatic compound in amount of 1-28% or benzene in amount of less than 5% benzene
 64. An unleaded motor gasoline base blend composition having a Motor Octane Number (MON) of at least 80 comprising component (a) 10-40% (by volume of the total composition) of at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 12 carbon atoms and less than 5% benzene, and said composition having a Reid Vapour Pressure at 37.8° C. measured according to ASTMD323 of 30-120 kPa.
 65. A composition according to claim 64 which also comprises at least one olefin of 5-10 carbon atoms, aromatic compound in amount of 1-28% or less than 1% benzene.
 66. An unleaded motor gasoline base blend composition having a Motor Octane Number (MON) of at least 80 comprising component (a) at least 5% (by volume of the total composition) of at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  I wherein R is hydrogen or methyl and at least one of isomerate, alkylate and straight run gasoline, which contains component (b) which is at least one saturated liquid aliphatic hydrocarbon having 4 to 12 carbon atoms.
 67. A composition according to claim 63 which comprises said olefin and 1-35% aromatics.
 68. A composition according to claim 63 of MON 80 to less than 98 which comprises at least 8% of triptane, component (b) comprising said hydrocarbon of 5 to 10 carbon atoms, and a liquid alkene of 5-10 carbon atoms, and optionally butane.
 69. A composition according to claim 64 of MON 80 to less than 98 which comprises at least 8% of triptane, component (b) comprising said hydrocarbon of 5 to 10 carbon atoms, and a liquid alkene of 5-10 carbon atoms, and optionally butane.
 70. A composition according to claim 60 of MON 80 to less than 98 which comprises at least 8% of triptane, component (b) comprising said hydrocarbon of 5 to 10 carbon atoms, and a liquid alkene of 5-10 carbon atoms, and optionally butane.
 71. A composition according to claim 68 which comprises at least one of isomerate, alkylate, aviation alkylate and straight run gasoline, which contains component (b).
 72. A composition according to claim 63 which also comprises at least one saturated aliphatic hydrocarbon having 4-6 carbons which has a boiling point at atmospheric pressure at least 30° C. lower than the hydrocarbon of formula I.
 73. An unleaded aviation fuel composition, having a Motor Octane Number of at least 98, and having a final boiling point of less than 170° C. which comprises: component (a) comprising at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  (I) wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 5 or 6 carbon atoms wherein at least 20% by volume of the total composition is a hydrocarbon of formula I.
 74. A composition according to claim 73 which comprises at least 30% by volume of the hydrocarbon of formula I, which is triptane.
 75. A composition according to claim 74 having a Reid Vapour Pressure at 37.8° C. of 38-60 kPascals.
 76. A composition according to claim 73 wherein component (b) comprises a component (III) which is more volatile and has a lower boiling point than triptane and a Motor Octane Number greater than
 88. 77. A composition according to claim 76 wherein component (III) comprises iso- pentane.
 78. A composition according to claim 77 which comprises 5-25% by volume of iso-pentane.
 79. A composition according to claims 76 wherein component (III) comprises butane and iso-pentane.
 80. A composition according to claim 76 wherein the fuel composition comprises 0.1-3.0% by volume of n-butane.
 81. A composition according to claim 76 wherein component (b) comprises in addition to component (III) a component (IV) having a boiling point higher than triptane but less than 170° C., and having a Motor Octane Number of at least
 92. 82. A composition according to claim 81 wherein component (IV) is iso-octane.
 83. A composition according to claim 73 wherein the composition comprises up to 30% by volume of an aromatic liquid hydrocarbon of 6-8 carbons.
 84. A composition according to claim 73 which comprises as component (I) said hydrocarbon having the formula I and a component (II) an oxygenate octane booster.
 85. A composition according to claim 84 wherein the component (II) is an ether.
 86. A composition according to claim 85 wherein the ether is methyl tertiary butyl ether.
 87. A composition according to claim 74 wherein 35-92% by volume of the total composition is the combined volume of the hydrocarbon of formula I and methyl tertiary butyl ether (if present).
 88. A composition according to claim 74 which comprises 80-90% of triptane, with isopentane and optionally butane.
 89. A composition according to claim 74 which comprises 30-80% of triptane, and also III isopentane and IV iso-octane, the volume ratio of III to IV being 35-15:65-85.
 90. A composition according to claim 83 which comprises 50-90% triptane, 5-25% isopentane and 5-30% toluene.
 91. A composition according to claim 90 which comprises 0-15% methyl tertiary butyl ether.
 92. A composition according to claim 74 which has a calorific value of at least 43.5 MJ/kg.
 93. A composition according to claim 74 wherein the Performance Number for supercharging is at least
 130. 94. A method of reducing emissions of exhaust gases in the combustion of unleaded gasoline fuels of MON of at least 80 which comprises having a compound of formula I as defined in claim 1 present in the fuel which is a gasoline as claimed in claim
 1. 95. A method according to claim 94 in which the fuel is a motor gasoline with a MON of 80 to less than
 98. 96. A method according to claim 94 in which the fuel is an aviation gasoline with a MON of at least
 98. 97. A method according to claim 94 to reduce emissions on cold start of a spark ignition combustion engine.
 98. Use of a compound of formula I, RCH₂CH(CH₃)—C(CH₃)₂—CH₃ wherein R is hydrogen or methyl, in an unleaded gasoline of MON of at least 80 as claimed in claim 1 to reduce emissions of exhaust gases on combustion thereof.
 99. An unleaded aviation fuel composition, having a Motor Octane Number of at least 98, which comprises: component (a) comprising at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  (I) wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 4-10 carbon atoms wherein at least 30% by volume of the total composition is a hydrocarbon of formula I.
 100. A composition according to claim 99 wherein the hydrocarbon of formula I is triptane.
 101. A composition according to claim 99 having a Reid Vapour Pressure at 37.8° C. of 38-60 kpascals, preferably 38-49 kPascals.
 102. A composition according to claim 99 wherein component (b) comprises a component (III) which is more volatile and has a lower boiling point than triptane, with a Motor Octane Number greater than 88, preferably iso-pentane.
 103. A composition according to claim 99 wherein the fuel composition comprises 5-40% by volume of iso-pentane, preferably 5-25% by volume of iso-pentane.
 104. A composition according to claim 102 wherein component (III) comprises butane and iso-pentane.
 105. A composition according to claim 99 wherein component (b) comprises in addition to component (III) a component (IV) having a boiling point higher than triptane but less than 170° C., with a Motor Octane Number of at least 92, preferably iso-octane.
 106. A composition according to claim 99 wherein the composition comprises up to 30% by volume of an aromatic liquid hydrocarbon of 6-8 carbons, preferably 5-30% by volume of toluene.
 107. A composition according to claim 99 which comprises as component (I) said hydrocarbon having the formula I and a component (II) an oxygenate octane booster, which is an ether, preferably methyl tertiary butyl ether or ethyl tertiary butyl ether.
 108. A composition according to claim 105 which comprises 30-80% of triptane, and also III isopentane and IV iso-octane, the volume ratio of III to IV being 35-15:65-85.
 109. A composition according to claim 104 which comprises 40-90% of triptane, an isomerate fraction comprising 30-70% isopentane the amount of isomerate being 6-44% of the composition, and in the composition also isooctane in amount of 10-35% of the composition and 1-3.5% of butane.
 110. A composition according to claim 109 which comprises 40-60% triptane, 6-17% isomerate, 10-35% isooctane, 1-3.5% butane, the isooctane being at least partly present in a mixture predominantly of iso C₇ and iso C₈ hydrocarbons with small amount of iso C₆ and iso C₉ hydrocarbons, said mixture providing 8-55% of the total volume of the composition.
 111. A composition according to claim 106 which comprises 50-90% triptane, 5-25% isopentane and 5-30% toluene.
 112. A composition according to claim 99 which comprises 1-30% by volume of a branched chain alkyl substituted benzene wherein a branched chain alkyl group is a secondary or tertiary alkyl group of 3-5 carbons, and there are 1 or 2 of such groups as substituents.
 113. A composition according to claim 112 wherein said substituted benzene is tertbutyl benzene.
 114. A composition according to claim 112 which comprises 2-7% butane, 1-15% isopentane, 50-90% triptane, 1-25% isooctane, 1-15% toluene, 5-25% of methyl tertbutyl ether or ethyl tert butyl ether, and 1-20% tertbutyl benzene.
 115. An unleaded aviation fuel having a Motor Octane Number of at least 98, and a final boiling point less than 170° C. which comprises: component (a) comprising at least one hydrocarbon having the following formula I R—CH₂—CH(CH₃)—C(CH₃)₂—CH₃  (I) wherein R is hydrogen or methyl and component (b) at least one saturated liquid aliphatic hydrocarbon having 4 to 10 carbon atoms wherein at least 20% by volume of the total composition is a hydrocarbon of formula I, together with at least one aviation gasoline additive selected from anti-oxidants, corrosion inhibitors, anti-icing additives and anti-static additives.
 116. An unleaded aviation fuel composition having a Motor Octane Number of at least 98 which comprises 1-30% (by volume) of component (h) a branched chain alkyl substituted benzene, having 1 or 2 branched chain secondary tertiary alkyl groups of 3-5 carbons, and (b) at least one saturated liquid aliphatic hydrocarbon having 4-10 carbon atoms.
 117. A composition according to claim 116 which comprises 4-10% of butane 0 or 2-10% isopentane, 45-75% isooctane, 0 or 8-35% toluene and 0% or 5-25% methyl or ethyl tert butyl ether, and 5-30% tertbutyl benzene.
 118. An unleaded aviation fuel having a Motor Octane Number of at least 98 which comprises a fuel composition according to claim 116 and at least one aviation gasoline additive selected from antioxidants, corrosion inhibitors, anti-icing additives and antistatic additives.
 119. A method of boosting the octane number of an unleaded aviation gasoline which comprises having present in said gasoline a compound of formula I or a branched chain alkyl substituted benzene having 1 or 2 branched chain secondary or tertiary alkyl groups of 3-5 carbons.
 120. A method of reducing the exhaust gas temperature from combustion in a spark ignition aviation combustion engine of an unleaded aviation gasoline, which comprises having present in said gasoline a compound of formula I or a branched chain alkyl substituted benzene having 1 or 2 branched chain secondary or tertiary alkyl groups of 3-5 carbons. 